This has to be done via the Billing and costs area in the Fee Earner Desktop:
From the LAD select Firm tab.
Select The Fee Earner Desktop.
Put in the Case reference.
Select Home tab, select drop down on Billing & Costs.
Select View and then the bill will come up.
Select the box at the bottom of the screen Retract.
This will retract the submission and mark the bill back to draft.
Once this is back at draft you can either select Delete or amend the draft to have the correct figures in and resubmit.