How do I zypper dup from a readonly snapshot?

4.16.6 doesn’t boot properly (black screen) so I booted from 4.16.3-1, which is a readonly snapshot.
How do I zypper dup to the latest TUMBLEWEED?
If I try to do it from 4.16.3, it won’t install because the filesystem is readonly.

Boot from command line - menu, 4.16.6 with “e” key, , put 3 at the end of the line with vmlinuz, boot with F10 (or ctrl-x …). From command line, log in your account and …zypper dup.

You clone read-only snapshot into writable one. It is called “rollback” although in practice you can also “roll back” into more recent snapshots.

rollback did what I needed.