You would want to use the EDIT function rather than the LEARN function. You get to it by MAIN MENU > DISCRIM > EDIT
Once you are in the menu, you can adjust the size of the "paint brush" using the upper left touchpad (select one of 3 sizes). Then, you use the navigation touchpads to position the cursor where you want to either accept more of the screen or reject more of the screen.
Bottom left = move left
Bottom right = move right
Center right = move down
Upper right = move up
[size=large]NOTE:[/size] Make sure the bottom box on the left side of the screen is blank; i.e., no X or Check when you move the cursor around the screen.
To accept sections, simply press the center left touchpad to get the CHECK MARK to appear and you will turn black to white. The opposite will reject white areas and turn them black.
To do what you are looking at doing, the best option is to use the smallest cursor and "chip away" at amy black you want to fine tune.
If you have the Explorer SE manual, look over pages 50 thru 53 for screen shots. If you do not have the manual handy, you can grab an electronic copy from Minelab's website using the link below.
Minelab Explorer SE Manual
I'd give you the page numbers in the book but I do not have one with me.
Let me know if this answers your question
Andy Sabisch