You need to relocate that betta ASAP.
1. Find a suitable CLEAN container. As said, it should be at least 1 gallon but as a temporary home less will do. You could use a large coffee jar, a Kritter Keeper... anything that is fish-safe.
2. Rinse it (the container, not the fish

) under running water a few times. JUST use water, no chemicals.
3. Use some substrate from your other tank for the bottom.
5. Use water from your other tank too, so the temp., pH etc. are the same.
6. Gently net the betta and put him in his new tank.
As soon as possible, go to your local fish store and get yourself a nice betta tank. Nothing too small, they like swimming room.
Hope this helps.
