How do I re-set my iPad when I no longer use the ISP I originally set it up with

The Apple ID used for my iPad was an email address and password for an ISP I gave up using sometime ago. I have no record of the password and various guesses have not worked. I want to re-set the iPad with my new Apple ID but can’t re-set the iPad to factory settings to do this. What can I do? If I take it to an Apple re-seller (I live in Kenya so no Apple stores) can they do the re-set or is there any way I can do it? I appreciate that if it was easy, thieves could do the same