You should contact the US Embassy where you are living or speak with your Congressional representative in the U.S. but likely, unless it is dangerous where you are, you and your partner will need to go through the standard marriage-based/fiancee process and having your partner enter on a tourist visa and then apply for a green card is legally impermissible and risky - although might be forgiven in the end.
All Embassies are still open; they're just on significantly reduced staff and only handling very limited matters but if you can't reach anyone, contact your Congressional representative.
Yes, I've spoken with them recently as have a number of my clients. And one of their focuses now is to help US citizens and their families who are abroad.
