Newt and Credence ran into King's Cross Station, where the note had said Grindelwald was holding Tina captive. In fact, it turned out that Grindelwald was chaining Tina to the railroad tracks!
"Well, this is a cliché," said Credence, recalling the many silent films he had seen while living as a Muggle in New York.
"So, you love the Muggles, do you, Scamander?" said Grindelwald, while bent over Tina, who still had those antlers, by the way. "Let's see how you feel about them after your precious girlfriend is killed by a Muggle invention! Unless you're willing to join me, that is." And then, his wicked act complete, Grindelwald looked up at Newt.
"Wait, hold up a second," said Newt. "Who are you?"
"Uh, I'm Grindelwald," said Grindelwald. "Your evil nemesis, remember?"
"No, Grindelwald looks like Johnny Depp. You look more like Mads Mikkelsen."
"I assure you I am Grindelwald... now."
Newt frowned and shook his head. "No, you're clearly a different person than you were the last time we met."
"Just go with it, Eddie!" yelled David Yates from off camera.
"Uh, okay then," said Newt uncertainly.
By the way, it turns out even Grindelwald would not be evil enough to deny that Biden won the 2020 U.S. election. This is canon now.