After pregnancy the Diastasis Recti should begin to heal within a few weeks to the point that you look better somewhat.
But it can take between 6 months to as long as a year or two for the Diastasis Recti to fully heal after pregnancy as it all depends on the person.
In my experience the Diastasis Recti I had after pregnancy went away fully within 18 months although a few weeks after pregnancy the Diastasis Recti started going away and I felt a bit better and looked a bit better after a few weeks.
You can have a Tummy Tuck to fix the Diastasis Recti surgically but usually it's just a cosmetic issue so you'll need to pay for the Diastasis Recti surgery out of pocket.
For me I just waited it out and the Diastasis Recti went away fully within 18 months time.