AppVM/HVM kill without snapshot

Question about snapshot reverting. Volume backup and revert | Qubes OS

If we have AppVM already running and at the same time we have 2 previous snapshots by default. (eg. 2020 and 2021 snapshots)

How to restore 2020 ? If we will shoutdown AppVM, this snapshot will be removed and it will be only possible to restore 2021 snapshot after shutdown)