If you would like to edit the Loss Reasons that appear on the Opportunity Screen, this is possible through the Settings menu.
Click ‘Settings’ in the menu panel, then scroll down to the ‘Lost Reasons’ dropdown and expand this. Then click ‘Add Lost Reason’:
Next, select the 'Brand' you want the loss reason attached to, then enter the 'Description' (this is the description that will appear in the dropdown on your Opportunity screen) and select whether details are required for the selected loss reason.
Finally, click 'Save' and your loss reason will be added to your dropdown options on the Opportunity screen.