Is it a hole or is it ripped? One of mine once got stuck behind the filter and she ripped it. As long as the water is fine it will heal by itself, it was all good within a week. If you want to you could try melafix, but I would wait first as they usually are self-healing with good water parameters.
Its either being predated by another fish, or its torn it on something. Keep the water parameters perfect, and keep up the regular water changes and he'll likely be fine.
Perhaps sit an observe its interaction with your other fish if you're worried something else in the tank has caused it.
I do see one of the snakeskins chase it for 2 seconds but they do the same thing with the other female guppy which i think is were they "show off" to it. My tapsafe says it has aloe vaya which adds a healing coat but i have to see if it keeps getting this problem otherwise it wont heal like you get a cut on your hand and it wont heal if you keep harming it