Here is the link to the test APK
You will likely also be asked about installing from an ‘unknown source’ and you are going to need to approve that.
Remember this is just because we are testing like this , it will install like any other app in the play store.
It is possible you phone will just download it and do nothing. You will need to then look in your notifications area for a ‘Download complete’ message and click the file called ‘app-release.apk’ there.