Could not find a valid GoogleService-Info.plist in your project

I had the same issue.

Click on the Googleservice-info.plist in your project and check Target Membership for app in the inspector. That fixed it for me.

That is the reason for this crash and removing the file and adding again is another way of doing as suggested by answers above. But the actual cause is this and this is the right way to solve it.

Please refer to the image below for further clarification:

Remove the Google-Info.plist file from your project and try to add it from your project folder's option menu.

EDIT: this is how you remove a plist file Xcode 10 Error: Multiple commands produce