Original!Graves is an omega. It's not a secret or anything, but a lot of people assume he's an Alpha/Beta because he uses suppressants (he has an important job, and no time for heats, thankyouverymuch), and because of his controlled, dominant personality. After the whole mess with Grindelwald, Graves is found, and he's in heat (on top of everything else), and it's not going away because reasons (Grindelwald did something? Magic?). Graves, who at that point doesn't really trust the people he works with (they didn't even realize he was gone!), asks Alpha!Newt for help him for reasons (Graves is friends with Newt's brother and knows Newt can be trusted? He thinks Newt's a neutral party and won't take advantage of him to advance his position? Newt helped alive!Credence, whom Graves was trying to take care of before getting kidnappend?) Whether or not/how Newt helps (sex? rare magical best ingredient? back rubs?) is also up to you, but both parties fully consent to it.