Click on JOBS on your top menu bar in MyTrucking and then go to FIND JOBS.
Simply tick the CHECKBOX shown on right hand side under Un-Invoice then click the Un-Invoice button at the top of then page.
A window will open asking for confirmation:

Once you un-post it, the job will move back to your Invoicing page in MyTrucking & you can edit the job and repost.
Note: you will need to delete your original invoice from your accounting package, to avoid a duplication of invoices.
Regards,
The MyTrucking Support Team
