Downgrade nvme pcie from gen 3 to gen 2

Running a pi 5 using nvme card but need to downgrade pcie from gen 3 to gen 2. How can I mount the boot partition to be able to edit /boot/confg.txt on hass os 12.1. In essence need to set this dtparam=pciex1_gen=2

Trying to mount /dev/nvme0n1p1 on /mnt/nvme/ that seems to be the boot partition but getting access denied using root