Please share exactly what you have tried to delete your versions and service, what documentation you have checked, any error or log you have. If your environment is standard or flexible and also it might be helpful to share which language you are using. Finally, make sure you have the right credentials to do it.
If you’re using Cloud SDK this document [1] might be helpful. Consider that you cannot delete a version of a service that is currently receiving traffic.
[1]:https://cloud.google.com/sdk/gcloud/reference/app/versions/deleteAre you using this command to delete the application?
gcloud app services delete SERVICES [SERVICES …] [--version=VERSION] [GCLOUD_WIDE_FLAG …]
You can also try this other on through the CLI:
gcloud app services delete {services list} --version=XXXX
Example: gcloud app services delete night-worker default day-worker --version=version2019
Here are some questions that you can find useful:
[2]:https://stackoverflow.com/questions/49021255/how-to-delete-an-app-version-from-google-cloud-platform
[3]:https://cloud.google.com/sdk/gcloud/reference/app/services/delete