If it is incorrect, please correct the documentation on https://www.group-office.com/wiki/Z-push_2.1 as I believe the folder is meant to be z-push21 and not zpush2 (as this is what I can only assume the correct folder to be).
3. rename the folder to "z-push21"
4. Copy the folder modules/sync/z-push21/backend/go/ to modules/z-push2/backend/
5. Copy modules/sync/z-push21/config.php to modules/z-push21/config.php