Rehabilitation for index finger

About 15 years ago I did a silly thing with a knife and sliced half my index finger off. After a couple year of physical therapy I now I have full mobility again and didn’t think any more of it.

Couple months ago I decided to learn the guitar and for the first time I felt a dull stiff pain in my finger. Does anyone have any tips or rehabilitation techniques they can share? Scared that I’ve messed myself up