If you find a bug in the live server installer, we might ask you to test the latest version of subiquity if we believe it has been fixed there. If you have internet access from your system this is fairly easy: boot the installer as normal, wait for the installer to start, drop into a shell via the help menu or control-z or f2, and run “sudo snap refresh --edge subiquity”. The latest version of subiquity will be downloaded and the installer will restart.
You can also boot with subiquity-channel=edge on the kernel command line, in which case the installer itself will offer an upgrade. Accept this and the new installer will be downloaded and installed.
If you do not have access to the internet access from your server, things are a little trickier. The subiquity source https://github.com/CanonicalLtd/subiquity contains a script ./scripts/make-edge-iso.sh which can be used to make a new ISO file containing the latest subiquity, which can then be dd-ed onto install media in the usual way.