how to unlock uk vodafone carrier

By contacting that carrier and asking them to unlock the iPhone, if you're eligible.

See this support article too:--> How to unlock your iPhone for use with a different carrier - Apple Support

Regards

Giulio

Sorry about that, but you have no alternatives, except those listed in the support article I already posted, and/or asking that iPhone previous owner to unlock that device. If he can't do that, give him back that iPhone, and ask for a refund.

Regards

Giulio

Vodafone UK = https://www.vodafone.co.uk/

AASP (Apple Authorized Service Provider): choose one among this list:--> Find Locations - Apple

Regards

Giulio