Your bit might be two lose in his mouth. I would tighten the cheek pieces to raise it up. Maybe. This could help prevent him from putting his toungue over it. I would also talk to your trainer, they should be able to help for it may have to do with you hand position or something else.
Thank you sierra, I have tried another bit and he ran right through it and wouldn't listen, he only started doing this recently and has been in the same bit for 2.5 years
Sometimes the bit can hurt the roof of your horses mouth with pressure where the bit breaks. Maybe try a different bit? I use a broken snaffle that breaks in 3 pieces rather than 2. This spreads the pressure more evenly