Got a Frozen Food Coldroom on R502 which due to leak on remote condensor has lost gas.

A company has been previous to my visit but no gas ID label is on unit. Exp valve is R502 so I will have to assume that R502 is what is in the system. Customer does not recall what engineer did on previous visit.

If I use R404A what oil do I need and do I need to do anything with expansion valve i.e orifice size (not sure of size at mo)?

Or is there another gas I could use that involves no oil change and minimal adjustments R407A for example?

Thanks