You should be able to reset your data by deleting your backup in Google Play Games. Here's some more info on it: https://support.google.com/googleplay/answer/9130646
Tap on Settings > Apple ID Profile > iCloud
Tap on Manage Storage.
Look for the game in the list of apps that iCloud backs up data for and tap it.
Select Delete Data. Note: This will delete all data for this game from all Apple ID connected devices.
If the above steps do not help then please reach out to the customer support team for assistance.