Betta Fish: Wound on Betta’s Side?

Hey, my fish Ralph is having a bit of a hard time. He’s a very accident prone fish, getting hurt and cuts more often than any other fish I’ve owned.

He’s is a giant koi half moon betta, had him for approximately 2 months, shares his 20 gallon tank with a loach with no issues.

I noticed yesterday and today he didn’t want to eat and has just been in his log hide, which was odd. I did a 30-40% water change which got him out of hiding when I noticed this on his side.

I have no idea what the next steps are. I haven’t been able to find anything similar to his wound online. Sorry for the not great picture, and had to take a screenshot of a video with flash on since I’m keeping his tank dark to lessen any stress. Any help for us would be greatly appreciated.