If you believe that for some reason a leave balance is incorrect. Here are some things you can do to check the validity of the leave balance.
Should the staff member accrue leave or do they start from a Balance?
Does the staff member have the correct tag that matches up to the leave type?
Is the starting balance correct?
Are the leave type rules configured properly?
Are other staff members having the same issue?
Check the calculation.
If the leave balance is incorrect and the everything else is correct, then recalculate the leave balance.