What can i do when my ankle brace is digging into foot arch?

Pad it : If the ankle brace is in fairly good shape you can try padding with mole skinsoaking or a thin foam. If the brace is worn out you just need s new one. Address the problem soon so you do not rub sores.

Depends: Some of the ankle braces are adjustable if it is that is one way, check to see if the size is proper. I don't know if it is directly on your skin if it is try putting your sock on first, you can try padding it as well with something like adhesive moleskin. Lastly, if all else fails get a different brand brace.

Have it evaluated: Try wearing an extra sock. The brace may be the wrong size. Have your physician evaluate it to see if you need a different brace or just a different size.