Driving license

I took my driving test in a automatic car however after a few months I checked my license and it doesn’t have the 78 auto restriction code, it has 74 which means I can drive manual cars. On my pass certificate it also says I passed in a manual car. What should I do?

You've got lucky there! It just means your instructor forgot to tick the auto section, so legally you can drive a manual car. Its up to you whether you want to start learning to drive a manual - i'd suggest practicing with a friend or family member who knows how to drive one first.
Legally you can drive a manual, so if you want to then practice and enjoy not having to pass a test again!