Try this stand and roll your foot on a frozen water bottle. Also foam roll your calves. Try the following Eccentric exercise! performed twice a day, every day for a few weeks, and done slowly.
https://youtu.be/VKYnPr6Tw5o
Is it the bottom of the heel? If so it could be fasciitis. If it is it can be very painful. I have tried all the suggested exercises with no relief so I had a reflexology massage which was for the lower body and legs and 3 months later I still have no pain.
I had what's called Haglund's Heel in both my feet but worse in my left. I'm not sure if it's what you're describing but normally you can see a bump on the back of your foot of where your bone is and it's very uncomfortable with most shoes. If any chance it is Haglund's heel I do not recommend surgery... does almost nothing and is VERY painful
I had this as well. Very painful and hindered my activity. I went to the doctor for it and was advised to stretch my calves a good deal and then take my foot/heel and press it against say the edge of a step (or something like that). It is a bit sore to do but I did recover doing these two things. They also make wraps for this now which I haven't tried but have seen advertised.