See Fair Work Act s.588
A person who has applied to the Fair Work Commission for an unfair dismissal remedy may discontinue the application in accordance with the procedural rules whether the matter has settled or not.
There are 2 ways to discontinue a matter before the Commission.
A signed 'Notice of discontinuance' [Form F50] can be filed with the Commission to discontinue the application. A copy of the signed notice of discontinuance must then be served on the respondent.
A matter can also be discontinued by advising the Commission, or a member of staff of the Commission by letter, email, fax, telephone or orally, in person.
Once filed a notice of discontinuance is self executing and it brings the application to an end.
An applicant, or their representative acting on the applicant’s instructions, can discontinue an application at any time.
In certain circumstances a notice of discontinuance can, in effect, be set aside if it was filed by mistake or under duress. In such circumstances, an application would need to be made to a court for a declaration that the notice was a nullity.
If an unfair dismissal applicant unconditionally discontinues their application before the Commission has determined it on the merits (ie without there having been a settlement of the matter), then they can make a fresh application in respect of the same dismissal.
This could be another unfair dismissal application, or if eligible, a general protections dismissal application or an unlawful termination application.
The subsequent application must be accompanied by the prescribed application fee and must be made within 21 days after the dismissal took effect (or within such further period as the Commission allows).
 Fair Work Act s.588.
 Fair Work Commission Rules r 10.