After you have created a letterhead, you need to link it to a template in LAWLIFT.
Open your template in the editor mode. Click on OPTIONS in the upper right corner. Then click on the field above the sentence "Assign a letterhead to the template for the document export" and select the letterhead from the provided list with one click.
You can now also display the templates linked to a layout under "Layouts Advanced" after clicking on "Edit" and also jump directly to the template by clicking on it.