As long as it's not in a wagesheet yet then you can change everything including the allocated skill and wage via Process Wages under Wages.
Check the box and use the update options at the bottom to change both the skill and the wages. You can update multiple at the same time.
If the wage sheet has been created but not yet exported for payment, then the wage sheet can be undone and the issue corrected.
If the wage sheet has already been exported then you will need to ensure that the destination payroll system is updated. You can contact the support team (firstname.lastname@example.org) to have the issue retrospectively fixed to ensure the reports are correct.