Television

I do not think it was in the book, rereading the book again (2nd time), because of the series’ changes, or the 1990 Mini-Series (my opinion best visual expression of ‘It’) & much later 2-movies (I disliked both, but keep giving them a try to impress me & they fail).
I liked the series a lot, even with gory bloody scenes (I hate those type of visual entertainment & never scares me, just grosses me out) & main, Kid, character dying, until the following changes that make no sense.
I hate it. Was never necessary,

Plus, I cannot see how ‘It’ can ever be defeated with that huge advantage.
No other character in the series is in Past-Present-Future at exactly the same time.

The Indigenous nation’s idea of using the pieces, of the spaceship-prison, to cage ‘It’ could never work. ‘It’ was only in the cage after the cage was created-when the stupid military General (correct me if I wrong about the character’s rank) freed it, when everyone else exists only in the present. ‘It’ existed when it was not built & after he was freed from the cage, at the very same time, “he was supposed to be caged”, thus ‘It’ was never caged & can never be caged.
Continuing with The Indigenous nation’s idea of using the pieces, of the spaceship-prison, to cage ‘It’, it makes no sense to the script’s/cannot be changed part about all expressions of the story of ‘It’ history, thus is another hugely stupid mistake. Simply, if the cage has existed for centuries before even 1908 (or someone wants to say just 50-years earlier/1858), then how the heck does, in every 27-years, ‘It’ escape? Again, If the answer is he exists in Past-Present-Future, then referencing the previous paragraph, the cage would never work.

Kill the kids when they are being born & feed on the fears of not threatening kids, until next set of threat kids are born, kill them & repeat to end of time. Some would say, the kids that threaten ‘It’ could be born & grow older while ‘It’ is in one or more of the times of 27-years of Hibernation. Remember with the super power of either existing at the same time in Or travels within Past-Present-Future, ‘It’ simply moves to the time when each set of threatening kids are born & takes them-out.

*- The Military General (again, correct me if I wrong about the character’s rank) reasoning to free ‘It’ & actually having it done, is just too unbelievably STUPID to accept. Forget that he also has to convince far too many military personnel below his rank to do it. He would just not be able lie most of the participating people into it. People would figure it out, especially, when destroying one of the pieces & the scientist. Maybe, there are a few certified crazies, but not the rest.

Now, the makers of this series should have simply-
Never had given ‘It’ the possibility to exist in the Past-Present-Future, at the same time or just as like a time traveler
&
Used military construction (maybe, building a underground <like a nuclear missiles [SP?]> facility) accidentally (**not believing the Indigenous Nation people’s telling them not to stealing there land to do it) setting ‘It’ free. Easily Believable, because it happened in IRW USA, many times.