Found an injured garter snake in my back yard, need some advice.

Hi I’m new to the group. And as the title states above, I found a injured garter snake in my back yard and need some advice on what to do.

The garter snake is about 16” long and has been living by my pond for a couple of years now. Just noticed today the garter is injured, I’m not sure how the garter got injured, but i believe it’s been in the last couple of days.
The injured garter has a open sore in the middle of its back and is missing part of its tail. The sore looks to be moving, like there is a parasite living in the wound.

Despite the wound on its back it dosen’t seem to bother him or her. Moving around quite well and looking for food. My question is should I leave him or her alone and monitor. Or should I attempt to help by catching the garter and try to treat the wound.

Thanks
Jay

Catching and treating would be helpful. Photos if you get the opportunity.