Are both the buns fixed?
My bunnys are still pretty shy sometimes but have outgrown it mostly, only being “shy” when they know its bed time or when they first come out and want to play.
Something I suggest to everyone as its what was suggested to me and it worked best for me. So, let the bun out alone so the other bun cant influence them, lay on the ground, and just focus on something other than the bun (a book, phone, newspaper, etc) If the bun comes up to you, sniffs you, walks on your back (my little bun is pretty light so it feels like a little massage!) just let her be. Don’t pay attention to her, don’t try to pet her, etc. Only pet her if she comes up and starts nudging your hand, but be slow and gentle.
cant promise it works, but, its what worked for me lol. It definitely wasn’t an instant bond, and did take a few weeks for her to get to the point where I could sit on the couch or the bed and she would come up to me wanting pettings