MS Access: Update data from one table to another based on a choice
Not sure what you want to achieve so let's start with saying that if you already have a table with the doctor's details, you shouldn't add them to the patientdetails table. If you need to display the data somewhere you can use joins in your query.

Thoughts:


Never duplicate data (unless you have to, these are only special cases)
You can always query data if they are linked (let's say you add the referring doctors id to this table)


example query

select * from PatientDetails join ReferringDoctors on PatientDetails.ReferringDoctorsID=ReferringDoctors.ID


Please provide more info, your current table structure, why you want to copy the info etc.