This is from IRS instructions: Forms 1042-S, whether filed on paper
or electronically, must be filed with the
IRS by March 16, 2020. You also must
furnish Form 1042-S to the recipient of
the income by March 16, 2020.
Copy A is filed with the IRS. Send all
paper Forms 1042-S with Form 1042-T,
Annual Summary and Transmittal of
Forms 1042-S, to the address in the
Form 1042-T instructions. You must use
Form 1042-T to transmit paper Forms
1042-S. Use a separate Form 1042-T to
transmit each type of Form 1042-S.