You can try to fix it with a silicone glue. I had a small tear in one of mine and it did the trick however, it dries shiny so hopefully you can find clothes or creative ways to cover it up.
I used GE Silicone II Household Glue & Seal https://www.amazon.com/Silicone-Household-Glue-Seal-GE280/dp/B001JK7OJA
Good luck!
>but it was in a sitting position for a while
This is probably the culprit. Leaving a TPE figure in a dynamic pose for long periods of time puts stress on the skin that accumulates over time. Which is why I tend to put mine away when I'm done photographing them. I haven't tried it with too deep a gash, but cyanoacrylate glue worked for some tears that developed on my 1/6 figure. Might be worth a shot, though do a spot test to be sure there aren't any problematic interactions. https://www.amazon.com/dp/B003Y49R7G
This is what was recommended: https://www.amazon.com/dp/B003Y49R7G
I've only had to use it a couple of times, but seems to have held up after a few months of posing. If you have to use it, wear gloves.