Tummy tuck reversal. Is there any procedure to loosen the muscles or reverse/cut the muscles?

No, this would not be a good idea. I can understand the psychological aspect of it, but an unnecessary elective surgery with all the surgical risks would not be in the patient's best interests, in my opinion.
I have not heard that women who have had a tummy tuck were not able to give birth in the normal way.

Dear nikki0808,
I understand your concern. However, without a proper assessment, it would be difficult to determine what went wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after a thorough examination, you can get proper recommendations and advice.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

During pregnancy your body will stretch slowly and naturally to accommodate the baby. Typically women can have a safe and healthy pregnancy despite a prior tummy tuck. If you are concerned I encourage you to discuss this with your surgeon.

Nikki,
I don't know where or what you are reading, but it is perfectly safe to get pregnant and having a normal delivery post abdominoplasty. Pregnancy is 10 months (40 weeks) and the abdomen slowly stretches as your fetus grows. I have had multiple patients have normal pregnancies and deliveries post tummy tuck.
Dr. Taranow