I stand to be corrected, but as I understand there is a fee for this of £122 together with a need to have to re-submit biometrics and some supporting documents.
The replacement of the Temporary Travel Vignette must be done by making a Transfer of Conditions application (TOC) online
Transferring a visa: ECB17
I've not done it personally so can't be specific on the process.
But since it's an online application and since it's expected that Biometrics will need to be done again I would guess that VFS would be able to assist in the detail.
Why not contact to the VFS folks and ask? might be quicker and more helpful than UKVI![]()