You are searching Kurviger Pro (Version 1.x)?
If you had it bought, then you should find it in the google play.
In an other thread there is a pictured guide (steb by step) in german language. Perhaps it is helpful for you:
Another guide in english there is in the operating guide to the app:
(For the info to Kurviger Pro (version 1.x) there you have to scroll a little bit to the end of the linked subtopic)
https://docs.kurviger.de/start?id=app/manual/general#app_kurviger_subscription_upgrade
Hope, that will help you to solve the issue.