I need help putting a bit in!?

Alright so I have a 14 yr old gelding named Frosty..He is great about putting on his blanket and saddle but when it comes to his bit...He hates it !! He closes his teeth so you cant get it in and he will move his head so u cant put it on and I am going to a show nd need to be able to put in in quickly...any advice ??