I’m making a 1x upgrade but I don’t know how to check if a chainring will fit, how do I check, I know my cranks have a BCD/PCD of 104 but my shop has said it may no fit my cranks due to positioning of the holes.

What cranks are they? If the holes are evenly spaced and not like M9000/M8000 they should fit if the same BCD. Some rare scenarios like m970 where they hade odd offsets but not an issue when using a single ring

my cranks are the Shimano Deore XT FC-M770

my cranks are the Shimano Deore XT FC-M770

Any ring with a standard 4 arm 104 PCD will work fine then

Thanks

Just done this on m wife’s bike. It fits fine