I want to draw ERD
You need to clearly specify whether a normal user can be an admin one day or not. However, we don't know from your description. This is a key point.
If a regular user will never be an admin you better use 2 different tables. If you want to use 1 table here are 2 solutions. The first uses the subtype concept which requires at least 1 different column between the two tables or that a subtype is a child table.
The data you provided does not show any different attributes between the two types of users, so you can't use the first solution based on the data given.
The second solution is more generic. If you plan to have the
RegularUser and admin changing types/roles, then you need to create an m-m relationship between RegularUser and UserType. (Note AppointmentID is PK for Appointment table).