"No, Vinda," said Grindelwald, suddenly entering the scene without any kind of setup. "We must leave now. We've run out of money."
"Oh, not this again!" exclaimed Vinda. "Just tell Warner Bros. they can dump this on HBO Max. Let's face it, we all know it's probably going to flop anyway."
"I was not breaking the fourth wall here," Grindelwald replied smoothly. "I was talking about the fact that the stock market just crashed and destroyed the fortune I made from my gumbo newsletter. The roaring '20s are over. It is now the threadbare '30s."
"What? But it can't be the '30s already, not when today's date is October 24, 1929!"
"Regardless, it's all over," said Grindelwald, "and now, we just need to get out of this mess while we still can. Oh, and we're taking back Credence." With that, Grindelwald ran forward and grabbed Credence before Newt could do anything to stop him.
"Hey, you're not Grindelwald," said Credence. "You look different."
"Aw shut up!" said the totally real Grindelwald. He then Disapparated, taking Credence with him. Vinda and Queenie quickly followed.
By the way, it turns out the Harry Potter and Lord of the Rings films now take place in a shared universe because they're both Warner Bros. properties. This is canon now.