Copy selected chapter file to 
C:\Users\yourname\AppData\Local\SpaceHulkGame\Saved\SaveGames, rename to "autosave1.sav". When loading in game, it will say that autosave 1 is going to be wherever you last autosaved it. However, it will instead load into the chapter you installed. Then you just restart the chapter from the game menu.

Chapter Saves

S1erra

Space Hulk: Deathwing

Chapter One

PlayStation 4

Shredmachine

DevastatorOne

Disciple

Disciple PS4/PS5

No Mercy PS4/PS5

No Mercy

1st Edition

Difficulty

PlayStation 5

Warhammer 40,000

TTInquisitor

Gorbish

wilderjoe

Rullmeister