Growing up in my dad's body shop and painting my fair share of cars, leaving it be is the worst advice, but sometimes repairs can make the issue worse if you don't take the proper steps in the repair! Having a pro do it can be the best advice depending on the "Pro" but any competent person can make a basic repair such as this with minimal tools and skill. Prep is everything and you want to remove ALL the rust (mechanically or chemically) and treat with a rust preventative before your preferred method of reattachment. Just use good quality materials from an automotive store or preferably am automotive paint supply store (NOT from Walmart or HF, etc.) and take your time and I am sure you will do a fine job.