- In the save editor, go to the RAW tab. In there, find the 'MissionPlaythroughs', and go into the collection.
- You'll see 3 'MissionPlaythroughData' on the left, the top one is PT1, middle one is PT2, the bottom one isn't used.
- Click whichever you want, then choose the 'MissionData' collection on the right.
- Then, just go through the missions on the left and select the one you want to reset/remove (the actual name will show on the right), and click on the big red X to remove it. You can now get the mission again from whatever gives it normally.
- Enjoy.