You’re wanting to safely get the mold and mildew smell out of your towels or other clothing items.
Luckly, there is a very effective safe solution to this. Vinegar. White Vinegar is both cheap and safe (you can use it in salad dressingings). It’s also a very effective cleaner especially when you need to kill mold and mildew. Put the affected towels or clothing items into the washer and use a quarter gallon of vinegar soaked onto the clothing items (that may seem like a lot but it’s always worked well for me). Now, run the washer once on warm or hot. When done with the first run your clothes will likely smell a little like vinegar. You’re going to run then a second time with your regular laundry detergent. When this is done, throw them in the drier and they should be as good as new (at least smell wise).