After "disable beta testing" in google play console, how to enable again?

My app is unloaded as beta release, tester can download and test the uploaded apk. After i pressed the "DISABLE BETA TESTING" button, and save it, the link for download apk become not available.

I don't know to enable the test again, because the "DISABLE BETA TESTING" button has not changed, it is always "DISABLE BETA TESTING", and I cannot found button like "ENABLE...", so, how can i enable the test to allow the download link available to tester again?