How do we gear our retainers?

[kaynide]

I tried that and it said "owned", wont let me get a second set.

I put a set in my chocobo bag, grabbed a second. (This was in Shadowbringers). Since 2 of my retainers are paladins, I had to go back and grab a third set. I assume the same holds true here as the separate inventories work independently (same as treasure maps, etc).