I do not have an Android device and don't really know how it works. I would expect that installing the snapshot version of Forge would be done exactly the same way you originally installed the release version on your device.
The download point for the file you want is here:
https://downloads.cardforge.org/dailysnapshots/I expect you need the one with a name sort of like: forge-android-202011230500-SNAPSHOT-signed-alig..
In the desktop version of the snapshop download, there are files called INSTALLATION.txt and MANUAL.txt with information on how to install the game. I expect the Android version is packaged in a similar fashion.
Some information about snapshots is found on this thread:
https://discord.com/channels/2673679461 ... 9265451029This thread is more specifically about Android:
https://discord.com/channels/2673679461 ... 7856883752On the forum we are on, there is this thread about installing the Android version of Forge:
viewtopic.php?f=26&t=22739In my experience with desktop, installing a snapshot is done in the very same way as installing a release version.
Hopefully something here helps.