First, don't refer to a person as "it." (There are exceptions, but this is not one of them.)
The pronoun "their" is used for the singular when the gender is not known, but if you object to that, then ask if people can submit their resume.
Second, because you have the modal verb "can" the other verb will take the bare infinitive (that is, the "to VERB" form without the "to"), "submit."
He sees it. He can see it.
She goes there. She can go there.
He played the song flawlessly. He could play the song flawlessly.
Can someone outside the U.S. submit his or her resume?
Student or Learner