Unfortunately you need the previous owner to deactivate it from their account, it’s meant as a security precaution against theft of devices.
I’ve see this suggestion in a couple of places but unsure if it works, other than that maybe contact Apple support to see if they can assist.
“Just but the iPod in Dfu mode. Hold down the home and power button for 15 seconds connected to the iTunes. iTunes will detect an iPod in recovery mode. Restore the iPod this will delete all the content in the iPod making it like a brand new device. Once it's finished you can sign in with your apples and use iCloud etc.”