Q: pls how can i unlock my iphone

Only the UK carrier can unlock it ,send it back to your friend and get them to have the carrier unlock it

Peter told you what to do.

If you choose to ignore him, your iPhone will continue to not work on your carrier.

And the advice given by Peter still stands. Send it back to your friend and get them to have the UK carrier unlock it. Only they can do that, not any one here and certainly not Apple.

and

UK carriers will only unlock for an active UK  customer using the iPhone in the UK so it is a brick where it is