http://dys2pwwos5w5kez2chufdk3b3oyj5n4n4iiseyke2tzuqahgvmovloyd.onion/en/2023-05-luks-security.html
Record that name, and run sudo cryptsetup luksHeaderBackup /dev/whatever --header-backup-file /tmp/luksheader and copy that to a USB stick or something. If something goes wrong here you’ll be able to boot a live image and run sudo cryptsetup luksHeaderRestore /dev/whatever --header-backup-file luksheader to restore it. (Edit to add: Once everything is working, delete this backup!