First, make a partition on nvme device with fdisk or parted, the partition will be under /dev/nvme0n1p1. Then, move your rootfs from sd/emmc to nvme with dd
dd if=/dev/disk/by-partuuid/b921b045-1df0-41c3-af44-4c6f280d3fae \
conv=sync,noerror bs=4M of=/dev/nvme0n1p1
Extend the filesystem
resize2fs /dev/nvme0n1p1
Edit /boot/extlinux/extlinux.conf
change
root=PARTUUID=b921b045-1d
to
root=/dev/nvme0n1p1
reboot and check mount.