Since it is not possible to specify a tax label in a manual journal entry, I need another way to post tax adjustments manually.

In my opinion there's only the function "Tax Adjustments", but i don't understand how this function works. How can I select the "Adjustment Tax"? This field is always empty. Do I need to configurate something first? 

You can reproduce this on runbot on version 9/10/11.

Thanks for your help