Easiest way to repair Retainer equipment?

Is there any way to quickly repair a Retainer's gear without taking it off of them? Btw, my only class is a Ninja.

Correct me if I'm wrong, but I don't think Retainer's equipment require any mending.

I think he must mean gear that he put in the retainers inventory that is damaged? Gear that retainer is wearing doesn't need to be repaired