At the end of the first IT, The Losers’ Club managed to best the ancient evil known as Pennywise.
IT: Chapter Two is set up to tell the second half of Stephen King’s novel, but it will include flashbacks to The Losers’ Club as kids.
After the final shot of the movie, we see that this first movie was billed as IT: Chapter One.
However, despite their victory, The Losers’ Club made a pact to get back together should Pennywise return in another 27 years, as he’s done in the past.