The auditor focused your attention in a particular problem, the non-conformity raised. Developing a corrective action means finding the root cause(s) and eliminate it/them.
First you have to expand your mind by answering to the question why. Why did this nonconformity occur?
A team can brainstorm a set of answers. The answers are hypothesis about what can be behind the non-conformity. Hypothesis are theories not the truth. Then, the most promising theories are selected, and information is collected, or tests are made to eliminate the wrong ones and keep the good ones. Now, we know what is behind the non-conformity, we know the root-cause(s). A root cause is something that has a strong impact in the occurrence of the non-conformity, and it is something that can be managed. It is time to develop a solution, something that will remove or reduce the frequency of the non-conformity. More than one solution may be available, normally one is chosen based on cost, or effectiveness, or easiness or resistance.
For example, during an audit a nonconformity was raised because there were no evidences of performance of a quality control during the night shift.
Why there was no control at the night shift?
Don’t like to do quality control;
Think quality control is not their job function;
Have no time to do quality control;
Actually, do quality control, but they do not record the results;
Don’t know how to do quality control;
Did not know they are responsible for quality control;
After some investigation. For example, what shifts missed the records? Who worked on those shifts? What kind of training did they had? You may realize that they never had training (hypothesis 5 and 2) because they were admitted in a rush to answer to a surge in orders.