Find the system.

sudo wipefs /dev/nvme0n1p5
# DEVICE    OFFSET TYPE UUID                                 LABEL
# nvme0n1p5 0x438  ext4 3899a753-aaaa-46e0-b034-cccccccccccc 
sudo mount /dev/nvme0n1p5 /mnt

Mount special filesystems:

sudo mount -t proc proc /mnt/proc
sudo mount -t sysfs /sys /mnt/sys
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev/pts /mnt/dev/pts

Change into the installed system:

chroot /mnt

Unmount the installed system:

sudo umount -r /mnt/dev
sudo umount -r /mnt/proc 
sudo umount -r /mnt/sys
sudo umount -r /mnt