What should you do if your recommender hasn’t submitted LOR near due date？

You should email the recommender a polite reminder. Something like:

I just wanted to touch base with you regarding my recommendation letter. Would you mind letting me know when you have sent them in so that I can cross them off my to-do list? It will help me keep my applications organized. As a reminder, my application for X is due, and Y is due _. Thank you in advance. I appreciate everything you're doing for me!