I have never worn a face mask in a grocery store. For more detail on that, please see my May 2, 2020, piece on this topic.
Many write me about this topic. The most common face mask request I receive is how a person can exercise an exemption at their grocery store.
This has worked for me every time.
Step 1.) Look up the store's phone number online.
Step 2.) Take out a pad of paper, write the date, time, and phone number.
Step 3.) Call and ask for the manager, writing down the name of anyone who says their name. If asked, your reason for calling is that you have a question about the face mask policy. If the person on the phone claims sufficient authority over the topic, just talk to them.
Step 4.) Say to them "I am unable to wear a face mask safely," may I still shop with you? I was thinking of coming by this afternoon.