You need to clean that thank out and fast.
you can't let uneaten food stay in the tank it will rot and poison the water.

Think about leaving a egg salad sandwich in your room for two days. PEW!!

That is what happing in your frogs tank.

If you act quickly you can save your frog.

I would get a clean plastic container and put clean treated water into the container and let that container float in the tank for 10 min to let the
water temp equalize. Then put the frog into the container and rinse out the tank with treated water until all the old food is gone.
Do not use plain water to clean it or you will kill the helpful bacteria that is in the tank.
if you have gravel that is small enough for the frog to get into its mouth this is the time to get rid of it and just go bare bottom.
this way it is easy to keep clean with a siphon.

Good luck.