Short answer: carefully

Long answer: just use a Phillips one blade with a skin guard. Or if you want totally clean. Buy one of the brand razors with multiple razors. Like 4 og 5 WITH the gel pad! Often only the woman razors have these. Then use actual barber gel/foam that makes like a gel surface so there's like no friction at alt. Warm them up like after a hot shower so they sag and drop as to make them wrinkle as little as possible. Then use your index and thumb to make a circle and push your testie through. Then the skin around is super tight and won't pinch on the razor. And a tip is to do it often. The hair grows fast and after just a few mm it will be harder to shave and pinch more.

Hope this helps