Enter a N or n into the Editing box, you'll see the two grids that make the glyph up along with a blank third grid on the bottom, add a small tilde in the top two rows. Or copy and paste the actual Ñ or ñ characters into the Editing box to create it new, and you can use it immediately with the alphabet textbox on the left.
Yes, and those glyphs don’t fit the grid. Try to redraw the n from the original font yourself. You can’t, because you can’t add points between the grid dots.
