If it is a case of creating a new invoice (or credit note) to reflect the rate adjustment, you can do this by creating new timesheets for each period of the adjustment, either with the difference between the old and new rate as a positive or negative amount (if you require a credit). These timesheets will generate invoices or credit as appropriate.
New timesheets can be created within the Incoming Images area by selecting the Add New Timesheet button or via the Create a Candidate Timesheet option, both within the Timesheet menu:
If you need to amend existing timesheets you can do this directly via the Timesheet Display option, but it is not always appropriate to do this retrospectively when sales invoice and payments have already been raised.
The Assignment Entry should also be updated to reflect the new rate arrangement. Please note the system will automatically apply any rate changes made to the Costings page of the Assignment to any timesheets that have not yet been processed, i.e with an Open status. If timesheets are mid-process you will have to update these separately via the Timesheet Display option or during the validation process.