This is quick and easy to edit. Go to Admin > Meals > Carry Balance Forward
Once you are in here choose your Year Group and which Academic Year you are looking at and click choose.
Find the student in question. Note; the Negative figures in green are credit and Positive figures in red are debt.
The Starting Balance is the field you need to edit, so click on the figure to edit and type the correct balance.
Click the little green tick to save and your starting balance is now updated.