How can i tag the invoice i created before i put the estimate price ?

Welcome aboard to the Community, @accounting389.

I can provide clarifications about linking invoices in QuickBooks Online.

Currently, you can only tag an invoice if you created it from an estimate. If you already created one, I suggest you delete it and follow these steps:

1. On the left panel, click Sales.
2. Go to the Customers tab,
3. Select the customer name. 
4. Press the drop-down arrow under the Action column to delete the invoice. 
5. Look for the estimate, the click Create invoice. 

I've included an article you can use to handle estimates, like how to link them to invoices:

• Convert an estimate into an invoice in QuickBooks Online

• Create partial invoices from an estimate

I appreciate you for taking the time to visit us here today, and I look forward to your response.