On this page of Marvel's Guardians of the Galaxy guide, you will find an answer to the question whether there is an option to repeat already completed chapters of the game (Chapter Select) and what rules are there governing such replays.
Guardians of the Galaxy does have an option to repeat a chapter, but unfortunately, this option is governed by rules that differ from most games of the genre. Repeat Chapter won't help you unlock additional achievements or obtain missed collectibles.
The most important information is that replaying chapters does not overwrite your previous progress. So you cannot count on the fact that with this mode you will be able to reach missed collectibles or change some important choices permanently. This means that:
- You should be careful when looking for secrets and making choices related to trophies to avoid missing anything. Here comes the ability to use 3 slots to save progress. Try to change the active slot regularly so that if you make a mistake, you can return to the previous moment of the game and play the last part of the mission again.
- If you miss something irrevocably without the possibility of returning or changing your decision, it is best to finish the game and then start a new campaign in the New Game Plus mode. Your found collectibles are there, and you can focus on obtaining the remaining ones.
The inability to save progress in chapter repetition does not mean that the mode is completely useless. You can use this mode to unlock trophies associated with combat, especially since some of them are related to the types of opponents that appear only in selected chapters of the campaign.