Before doing anything get the OK from your Dr.
I suggest also seeing a nutritionist.
As for the exercise try the following as long as your Dr.
Says it's OK to exercise!
Strength Training
Once you receive clearance, you can begin a wide variety of exercises to re-firm the abdominals. These include the basic crunch, bicycle crunch, supine bridge and reverse crunch. As you begin you should exercise until fatigued or until you complete eight repetitions of each exercise stopping at whichever comes first. After a week, you can work up to 12 repetitions and then eventually up to 20 repetitions once your rehabilitation is complete. Exercises should focus on the rectus abdominus, internal obliques, external obliques and pelvic floor.
Cardiovascular Exercise
Cardiovascular exercise will allow you to lose any fat that may have accumulated around your middle due to weight gain. Physical activity after pregnancy has been shown to decrease postpartum depression. All early cardiovascular exercise should be at a lower intensity than you would have engaged in before your pregnancy. Your endurance must be built up gradually to allow your body to fully recover.
If you Google the exercises I stated above you should be able to see how to perform them.
Of course we don't know the state of your recovery. I'd think your OB-GYN would be a good source for this question.