Hello Carl, as Mark says. Taking it back ( bought reasonably local?) is really your only option, since you must (1) give them the opportunity to repair it. (2) you cannot get anyone else to attempt to fix it, without the seller’s permission.
It could indeed be an ABS sensor - but which one of the 4? Diagnostics will be necessary to determine that. May not simply be the sensor ( which obviously senses a signal) but could be ( in addition) the actual ‘signal sender’ which is often built into the wheel hub.
Perhaps you could let us know how things pan out Carl.
Kind regards,
Gareth.