You need to register with ePay (mobile or web), go to "Excise & Taxation Department" then "transfer of motor vehicle" section. Provide vehicle registration number and buyer's CNIC, you will get PSID against the due amount.
Payment can be made through almost all online banking service using PSID. Once paid go to any "Nadra Sahulat" and seller can do biometrics against the invoice paid. Buyer's can do biometrics from anywhere as well.
After biometrics, vehicle inspection can be performed on selected excise office during application.
Buyer will get new registration card via courier or can collect by visiting selected excise office. That is pretty all I go through with my last transfer.
For more details: "https://excise.punjab.gov.pk/system/files/Advertisement_0.jpeg"