Generally TV shows have A, B, C plots, so the first thing is excluding the B and C plots and structure the narrative in the main A plot. When it's a miniseries or a serialized story it's much easier to fit in a 3-act structure because you just need to take out the filler and arcs inside the season that are done to be mid-season filler etc. Montages are also really welcome to situate episodes that impact the story but are just 50 min one-shots. And as others above mentioned, be absolutely unsparing while cutting stuff. Even if the scene is good, if it dosen't impact the story or the main charachter at all just throw it away. That could be anything from lines of dialogue all the way to entire episode arcs. A TV-to-Movie edit has to be purely meat and bones, no fat whatsoever.
The problem is when you have a procedural series like
The X-Files when every episode is a one-shot story that links into a greater universe (think of MCU in that regard) you won't be capable to nail down an 3-act structure, since almost every episode has its beginning and ending so the thing in this case is to construct an almost anthology structure while at the same time being cohesive into the flow of the narrative.
The best ones I can think of are
Andreas Game of Thrones franchise,
It'sOnRandom Breaking Bad movies (honarouble mention of Breaking Bad: The Movie which condenses the entire show into a 2 hour movie),
Adabisi The Beast in Me,
Gieferg The Witcher series, and the Sherlock movies by ranger613, theryaney and
Zarius . These are all examples you should follow, IMO.