Undeleting a question does not 'bump' it in the system, which is by design, because deleting, and undeleting a question should not be a way to 'bump' your question.
Similarly, editing a deleted question, and then undeleting it, would allow for users to completely change their question, and then, because the undelete would not bump the question, it is unlikely that the revised question would be significantly 'reviewed'. It would be a way for people to 'game' the system by introducing content that may be harmful.
So, you can't bump a question by undeleting it, and as a result, you cannot edit a question when you deleted it.
The solution is either:
- create a new question with the new content.
- undelete the question (no bump), then edit it, with bump.
In your case, I recommend editing the new content in a separate editor, then undeleting, and editing the new content in immediately.
The reason for this suggestion is that leaving your question deleted will count negatively toward the 'soctratic' badges.