TMEP § 1613.03
The holder must file the §71 affidavit or declaration through the trademark electronic filing system, unless an exception to the requirement to file electronically applies. See 37 C.F.R. §2.23(a); TMEP §301.01.
See TMEP §1613.04 regarding the deadline for filing the affidavit or declaration and §1613.05 regarding the requirements for filing the affidavit or declaration.