I have For The King on both Epic and Amazon stores. I installed the Amazon version so I don't have to run the Epic store to play the game. I added the game manually, but since it knows I own the game on Epic, I can't launch it just an Install button.

How can I link the executable of a game installed manually, when I also own it on a store that has a Galaxy plug-in?

I guess I could disconnect Epic, but that's not really a good solution.

Having the same issue with some games I bought in a itch.io bundle. Sadly no soultion as of now. The "epic" integration doesn't even allow custom installer. Well, no harm uninstalling epic. Not using their service anyway for some time.

@LordCephy For me there is no option. The second option always defaults to the one that is set as the current primary game release.

For example an already installed version gives me the Play option, a game that is not installed gives me the Install option. Even if its my console version.

Did you try this with an already owned game?

Did you used the arrow keys to highlight the selection ? This is the important thing to see the "Mark as owned" button, you can't see that button using only the mouse.

I did this with Minit, which is a game that I have through Epic as a free giveaway and itch.io as part of a charity bundle. If run through Galaxy, the epic version launches the epic launcher to launch the game. The itch version just runs. Where you have Install, I had a Mark as Owned option.

Also I've since disconnected Epic from Galaxy as I really dislike Epic's launcher.

In response to the OP: At the top of the game page should be a little diamond with a number next to it. This signifies how many versions of the game you have and if you click on it you can select between them. If you change it from "Epic" to "Other" then the install button will be replaced by a play button.

This should help anyone else who has the same issue as the OP.

Yes, I have. Did you try adding a "Other" game entry to an already owned game through another integration like GOG or Epic? Could you show a screenshot? You get this because you probably have an itch.io integration. Could you try adding a "Other" game entry through this means? With screenshots at best. You can't change it, if you don't already own the game as "Other". You can't see the diamond if you haven't marked it beforehand (or own it through another shop). Which you can't if you already own the game elsewhere. Unless you can show me with a screenshot.

Unless there're different versions of Galaxy, all these solutions don't help the problem if you own a game already and haven't marked it as "Other" beforehand.

After all these 2 years since all GOG essentially did was adding Epic to Galaxy. I'm not convinced there's much in the making anyway. So I jumped ship to Playnite (https://playnite.link/) which does a way better job at adding new games, updating metadata, grouping duplicate versions (through an addon) and much more. The integrations also work for more than a week without crashing.

I don't use integrations, but I am able to add a local game even if I already have installed it with Galaxy (in my case is useful because one folder is MODDED while the other is the original), and I have a switch icon at the top of the game page to choose what should run between the two.

I suppose you are using the wrong function, your screenshot shows the options you get if you use the normal "SEARCH" (CTRL+F), instead you should use from the main menu (top left) "Add games & Friend -> Add a game manually" (or click the "+" icon at the top of the library), then search the game there.

The window is the same for both functions, but only the one for adding games shows the "Mark as owned" button.

EDIT:
added screenshot

I'm not on my PC right now, but I indeed always have used the default search when adding new games, that I didn't own anywhere. It's weird to me that both functions seem so similar, but are slightly different.

That should help the OP and anyone searching for that option. For me it's Playnite, but thanks for the answer!

He clearly states in the OP that he added the game manually so it is already "Other", what else do you take that to mean?

I was searching for a way to do this and found this topic, which didn't help of course (none of the answers has anything to do with the OP issue).

So I found a way, and I'm posting here so it may help someone that also find this topic in the future:

- Instead of going to the "search games" window (CTRL+F or magnifying glass), go to the cog icon > Add games & friends > Add game manually (might be other words since I use other language).

The windows look very similar, but they are slightly different. In this panel when you search for a game you own, it will show the option to mark as owned (instead of the "show game" option), and it will create an "other" option that will allow you to link an executable.