2 yr toddler has ingrown toe nails. Has always preferred to walk n jump on the toes like ballerinas. Doc suspects infection. How to stop him walk on toes?

Needs evaluation. 1st thing is that your toddler needs to be evaluated to see if there is a medical reason he walks on toes such as short achilles tendon or equinus. If not then exercises may be needed.
Time may improve it. It is not uncommon for some kids to toe walk some of the time up until 3 yo. By that point most abandon the practice. I usually suggest the parents flex the forefoot upward in a playful way to identify any tightness in the tendon in back.It should flex up without restriction or be evaluated and treated by a pediatric podiatrist or pediatric orthopedist.