How to manually setup the ios symbol uploads in a 2-flavor project?

[rivella50]

I have just added Crashlytics to my existing Flutter project with the 2 flavors staging and production.
The Android part works fine out of the box.
Since i couldn't call 'flutterfire configure' (my firebase_option files are located under lib/config) i get the message to upload missing dSYM files in the Crashlytics iOS area.

I do understand how and where to add the missing upload calls (Target Runner -> Build Phases), but since i host my 2 flavors within the same Target Runner i wonder how the correct upload calls are performed if i e.g. build for the staging environment, and therefore the scripts should be called to upload the symbols to the Firebase staging project?

Since i didn't find a documentation which covers this aspect i ask here and hope you can give me an answer.
Worst case would be to call those upload scripts in a terminal whenever i build a release to be distributed.