Unfortunately you need the previous owner to deactivate it from their account, it’s meant as a security precaution against theft of devices. Your best bet is to contact the previous owner and have them reset the apple id/password through https://iforgot.apple.com/password/verify/appleid There are a number of threads online with the following workaround, but not sure if it works.
“Just put the iPad in Dfu mode. Hold down the home and power button for 15 seconds connected to the iTunes. iTunes will detect an iPad in recovery mode. Restore the iPad this will delete all the content in the iPad making it like a brand new device. Once it's finished you can sign in with your apples and use iCloud etc.”