@RB2021 You must log on your rasp through ssh (putty.exe by example) and follow the indication written before.
You might find your rasp IP on your network, on the Recalbox UI or by other means.
Default credentials are well known by all (root / recalboxroot) but i'll advice you to change them later on
You'll need to know a lil' bit about how to modify a file with nano but i guess it can be handled even without documentation.
I'm not myself a linux master, far from it, i'll try to add some precision on how i handle theses :
Step by step
mount -o remount,rw /boot
#It allows enough permission to proceed
#It open the config.txt file with the nano tool
search for dtoverlay=vc4-kms-v3d and modify with dtoverlay=vc4-fkms-v3d
#You'll have to navigate into the config.txt to find the following info and change it
Save file (Ctrl + o)
#For myself, i do CTRL+X (to quit after change) , then Y (to say Yes to over write file), then enter to get out.
#Just type it in, or reboot by other means
Hope it helps ya ! From the noob i am too