How to restrict a PC for only one domain user ?

Hello there, I am new to system administration and recently implemented Active Directory in my work environment. We are facing a problem to provide security for some users (HR, Accounts etc,.) The case is, only a single user (User1) should be able to access particular PC (PC1). No other domain users like (User2, User3.. etc.,) should have the access to login to PC1. But Domain Admin should have full permission on that pc1.

Please help.