I can't give you a personal recommendation, but if you go to Viator and search for walking tours you may find something. Click on any that sound interesting, then scroll down to "Additional Information" and click there. Buried in that section you'll find the name of the company running the walking tour. You can then try to find their website or Facebook page and book directly, if they are operating tours now.
I will say that even traveling in the summer, I found that English-language walking tours in secondary cities didn't always operate every day. They were sometimes weekend-only.