Chapter 9102 (No precious watches)

Good morning community of this forum!
I am an Italian citizen and I have sold a used watch with titanium case to a UK citizen using an online platform.
I have to send to this person the watch and I would like to know if there are VAT or duties to pay for this operation.
I would like to use a private courier for the shipment, what have I to do for the HMRC?
Thank you for Your attention! I hope to receive help from you as soon as possible because I have to arrange for the shipment in few days and I don’t want to give problems to the buyer.