First of all while entering the patient name in the software itself you have to choose the referral source. 

If the Referral Source is empty, if you have not entered any referral source earlier, then click add new referral source

If you choose patient as the referral source, here you cannot manually enter the referral names, as patients name are already in your database.

Now to send the referral thanks letter to the doctor, you have to enter inside the patient profile, and just send the ready made template in just two simple steps. 

Now just choose the options to send the referral thanks letter, 

like SMS or Email. 

soon we are going to incorporate "Whats app" messaging.