How do I get another persons Apple ID completely off of my phone

What to do before selling or giving away your iPhone, iPad, or iPod touch [or if you received one that had not been erased] - "Use these steps to remove your personal information from a device, even if you don't have it anymore." --> https://support.apple.com/HT201351

If Find My is set you will need the Apple ID and password that was used to set it. There is no way to work around this. Get the previous owner to remove it or ask for a refund.