@yourrid in lr-genesis-plusgx you are supposed to be able to switch between 3 and 6 button with the select button but it doesnt work. And strangely some 6 button games default 6 buttons and some dont. So i just use lr-picodrive. Problem solved.
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first