Rapair muscle around belly button?

I have health problems that requires me to have sub-q infusions each week. I had been doing them in my stomach (on either side of my belly button) for around 3 years. I recently started doing it in my leg because it seems like the needles or the swollen bumps that I get after have caused my stomach to lose muscle tone. So, does anyone know what I can do to help repair the muscle right around my belly button? Maybe some exercises that really focus right there? I do sit ups, crunches, and planks all the time in my workout but they don't seem to help much there.