Link an invoice with a delivery note after both

Hello, how do i link an invoice with a delivery note after both have been validated without canceling it.

For literally linking both the documents, you should create Sales Invoice from Delivery Note or vice-versa.

If they are not linked directly, but indirectly via Sales Order, then based on billing, the Billing % will be updated in the Delivery Note as well.

To link document, you will have to cancel and amend it.