Open the MTM software, go to File menu -> Diagnoses and click the Add button.

Add the diagnoses you need, typing in the code and an abbreviated description. Use a combination of upper and lower case, not just upper case. NB: Psychologists must be careful to phrase the description sensitively as it will be printed on the account.

On the Patient Account Details screen do not simply type in a diagnosis. Select from the drop-down box and you will see the ICD10 code typed to the left of the diagnosis box on the screen. Now when you invoice then this code will come into the ICD10 box on the invoice window.
When you print an account the code will be printed in front of the description.
EDI batches will now include the code in the designated place.

If you normally change the procedure description, for example adding am and pm for 2 sessions per day, then do so at the front, not the end, of the description. You can also make use of out time entry system for this.