How to Fix my Separated Stomach Muscles and Tighten the Extra Skin. Are There Exercises I Can Do to Fix the Separation?

No matter how many situps you do, muscle separation cannot be fixed. This is because it’s not the muscle that’s been stretched - it’s actually the connective tissue between the muscles binding them together that’s been stretched. Only surgery can repair this.

unfortunately no....The muscles have been stretched and pushed apart and to the side and while you can make them stronger with exercise, you cannot move them back into the middle...That takes stitches!!!! And a lot of them!!! And as far as the skin, think of drooping breasts after breast feeding. No amount of weight lifting can get breasts like that to go uphill....again...more stitches....

Separation of the muscles in the middle of the abdominal wall is called rectus diastasis.  This occurs because the connective tissue between the muscles stretches during pregnancy.  This connective tissue, once stretched, does not come back to shape so the muscles are no longer held right in the middle.  It is possible to learn to contract those rectus muscles to bring them back into the center, but once you relax, they will slide back out to the side.  It is not possible to keep those muscles contracted all the time in this fashion.  Only tightening that connective tissue between the muscles will hole them permanently in the proper position and rebalance your abdominal wall.  This is done with a tummy tuck

Unfortunately, there are not any specific exercises that will correct rectus abdomens muscle diastasis ( separation of the vertically oriented muscles along the midline). You would likely need a full abdominoplasty ( tummy tuck) to correct this. You should consult with a board certified plastic surgeon option the options that would be appropriate for you.