There's a rubberband exercise you can do to strengthen the tendon, but I never had the patience. Put it around your fingers, then extend them for like a thousand reps. Also, squeezing a rubber ball. Again, thousands of reps over maybe three sets.
I'm exaggerating, of course, but I just never could handle the high rep therapy. Anyway, those two therapy exercises are somewhere online if you're interested.
Sorry, bro.