Add a label (tag) to the feed in Google Merchant Center

It is necessary to replace the label in an already existing feed or show how to add a label to new product feeds. I cannot figure out how to do this in the account, as the already created feed does not allow direct changes to the label, and when creating a new one, there is not even a field for the label.

It needs to be explained how to do this, provide instructions, and there will be no need to access my account.