I.G.
You will need to speak to your doctor. Hernias can be serious or not and some are serious enough that they must be treated, pregnant or not. Sometimes they can be treated conservatively without surgery, sometimes minimally invasive surgery is an option, it depends on the size, location and complicating factors.
Diastasis recti itself is not a hernia, though it may look similar. It is a very common side effect of pregnancy and can be managed without surgery, depending on the seriousness. It happens as the baby grows and stretches out the connective tissue that connects your abdominal muscles. It should not have any negative effect on your current pregnancy. The surgery to repair it is basically a tummy tuck and most good plastic surgeons will ask to to wait with this until you are done having children.
Good luck!