I thought I had written a Howto on that already but after some searching..... Looks like I didn't. 
I added the link in the Howto https://forum.elivelinux.org/t/resetting-password-using-chroot-on-encrypted-lvm-filesystem so as to make it findable when searching the forum.
In time we could add a specific Howto ourselves if needed.
I mean, who would look for LUKS password changing under "dynamic fonts"? 
