Bought MacBook pro last owner never reset how do I reset system so I can use

Your use of reset might be ambiguous, but I take it to mean that the previous owner has not signed out of iCloud and you therefore cannot sign into iCloud, rather than the other possible meaning that it needs the drive erased and a fresh macOS installation.

This is called activation lock and unless you can contact the previous owner the computer is useless to you. These are the options for removing the lock, including the previous owner removing it remotely at www.icloud.com