Treatments can be added to a wildfire both by searching a buffer around the fire and selecting treatments, or by adding the treatment from the map interface. These instructions describe the latter.
From the Layer List, click More Options to the right of the treatment layer name, and ensure "Enable Pop-up" is selected from the drop-down menu.
Scroll over the treatment and left click it.
In the description that appears, use the Add Interaction option to add that treatment to the list of interacting treatments for that fire.
If the pop-up contains more than one treatment you may browse these using the arrow in the top right of the pop-up as displayed below: