To add a professional to Client location, First Create a new professional if it is a new professional - (Please refer to this link What is a Professional / Create a Professional)

If you want to amend an existing professional to a client, please follow the instructions below 

Go to   

Logins > Professional Login


Select professional  from the list and it brings up the screen shown below 

Once you  see  the newly added Client Location in the above list, from then the professional will be able to book shifts for that client location.