Since you already hold an ATP, you can self certify for the exams, but you still have to take them. You can self study but it is recommended to use some sort of ground school course and question bank. You can take the practical in a sim for an airplane that you are already typed in.
You'll also need the class 1 medical, and he initial has to be done at a specific facility. I'm the U.K., you'll have to go to Gatwick. Renewals can be done with any approved AME.