On the Options Menu select the A2A IRIS option under the Filer Information section.

TIN: The Tax ID used when you created your Transmitter Account
IRIS TCC: This is the A2A TCC (not the portal TCC) See Getting an IRIS TCC.
Full User Name: This is the user name provided to you when you register your Consent for the Magtax application to communicate on your behalf. See Getting an IRIS Full User ID
TEST - Future Implementation. This will perform a Test Communication with the IRS IRIS Test System to verify communications.
Starting Submission No.: Submissions must be in sequential order. There are a variety of possible scenarios where you may need to re-sequence. Contact support to discuss. Otherwise Leave as 0 (zero).
Complete the rest of the form per your TCC account registration.
Also see