This is for "Small Lots of Seeds", but you can follow the procedure (and you can check plants in addition to seeds): https://www.nargs.org/small-lots-seed
Two things to note:
1. For "Regulated Article Name" pull-down menu (= which plants you plant to import), scroll down to the bottom, and select "NONE OF THE ABOVE". Then type in "Eligible Taxa".
2. "Country/Countries of Origin": no need to select anything. Then type "Various Approved Countries" in "Other County/Countries Name(s)" field.
NARGS site mentions that you need to visit a local USDA office to get Level 2 eAuthentication. But they can confirm your identity over the phone now. They will call you and ask a couple questions about yourselves.