Archlinux - LVM on LUKS - Reset Password
Boot into a live usb
fdisk -l
to find your encrypted partition
cryptsetup open /dev/nvme1np2
to decrypt the partition and show the logical volumes
mount /dev/VolGroup/root /mnt
mount's the root folder's logical volume (assuming you followed mine/the archwiki's default naming scheme)
arch-chroot /mnt
root into the mounted root partition
passwd user
change the password.