Inventory Price Increase

The products we sell increases yearly and I am required to update same on system - this increase does not affect previous products sold before price increase but affects all items as from 1st October 2021 - How do I change this as there are no furncion in Inventory for the date this would come into affect

You just change the Sale price on the Inventory item

Would this not affect ould invoices? aready done?

No

Thank you so much for your assistance