i cloud is disabled

A year ago a friend of mine gave me an iPhone as a gift when he came to my country.I didn't know much how iPhone operates at that time so the guy left without erasing his data on the phone.when I tried to use the phone I ended up on activation lock and started to read how to solve it.I had to contact him to erase the phone from his account and he did it for me.The good news is it passed the activation lock but I cant use the device with it's all features.There is an apple id of his which is still in the phone which wont let me erase the devise,sign out ,turn off find my iPhone in fact all the menu inside setting i cloud are grayed out or disabled so I am still using it as an iPod to listen music and use some application what shall I do?