Use hydrocortisone cream after manual stretching to help the healing of the skin especially.
You want to grip inside structures of the penis when doing manual stretches. The OK grip isn't best for that. Try using more fingers and curl them around so the fingertips poke into the meat of the penis. Grip the inner structures this way. You're not trying to stretch the skin only. You really want to grip and sttretch what's under the skin.
The OK grip is good for jelquing. Thats an erect or semi erect girth exercise. Basically its like a slow, tight masterbation type move to push blood towards, the head. This needs lube. Vaseline is best. Its okay to pull the skin along a little but you might use your other hand to withhold the skin to the base so your not over stretching skin and get what's called Turkey neck.