You can reverse the visits generation by following these simple steps.
Click Planning, then click Generation.
Click Visits, then select the relevant Branch.
Click the red bin beside the generation to delete the visits generated during that period.
Enter 'confirm' in the box.
If this does not allow you to be linked with a payroll or invoice, you will need to unaccept all periods in the invoice and payroll to the date you wish to delete. This will then allow you to remove the shift Generation you wish to remove.