Try this arm toning workout that avoids added pressure on the belly tissues where ab separation occurs (aka diastasis recti).
Diastasis Recti: Prevention and Exercise
Healing Diastasis Recti
Diastasis Recti - How to Train Clients With Diastasis Recti
Exercises for Diastasis Recti Relief
Exercise in the Fourth Trimester: What to expect and beyond
What to know about diastasis recti
Diastasis Recti Safe Ab Exercises - Moms Into Fitness
Diastasis Recti - How NOT to fix it (and what WILL work)
10 Diastasis Recti Exercises for New Moms - Live Love Fruit
Diastasis Recti Exercises to Try After Pregnancy