Hi oleg210448,
Welcome to Community! Taking advantage of the Tags feature in QuickBooks Online, is a great way to track invoices, expenses and bills. I would be glad to assist!
If you've created Tags, you'll be able to select the appropriate tag on your forms. You can also create a new one, by typing the name in the Tags field then select +Add. If you've already established a list of Tags, but don't see the field on your forms, click on the gear ⚙, in the top right and place a checkmark in the Tags box.
Should you require additional assistance, please don't hesitate to contact us. It would be our pleasure to work with you in real time, and review the issue in more depth from our end.
If you have any other questions or concerns, feel free to reach out. We would be happy to help!