To take actions after a survey you need to understand the problems behind the survey-score. You can only improve the score if you know why they are low.
Given a classical employee engagement survey, focus on:
Categories with the lowest score
Categories about relation to the direct manager
Categories about retention "do you see yourself in 2 years here"
To understand the reason for the score, study the comments. The comments provide details why an employee has given a high or low score.
You can use sentiment analysis or feedback analysis tools to analysis large amounts of comments.
Involve the employees with workshops and discussion-rounds to validate your understanding.
If possible collect concrete examples of problems.
Once you have the context and the detailed understanding of problems you are in a good position to find the right actions.