How do I change cocoapod dependency of a pod? (Firebase and GoogleSignIn not compatible)

I use Firebase and Google Sign In in my Unity project. The project is built both for Android and iOS. I do not make use of Google Sign In on iOS though.

Firebase latest versions, which I need, depend on GTMSessionFetcher/Core >= 2.1. Google Sign In, which is automatically included in the Xcode project (since it is integrated for both Android and iOS in the Unity plugin), depends on GTMSessionFetcher/Core that is lower than 2. So I cannot install both Firebase and Google Sign In (which I don't even use).

Is there a way to manually change the dependency of Google Sign In to a higher version of GTMSessionFetcher/Core, so I don't have pod installation issues? Like I said, I don't care if Sign In works or not.

Or is it possible to remove the iOS side of the Unity plugin completely without hurting anything on the Android side?

I've deleted some iOS-specific stuff from the Unity project manually, put all the Sign In code into

#if !UNITY_IOS...#endif

but the Xcode build gives "Build input file cannot be found" errors.