That is called: "mode-osu-small".
Find that image file on your skin and put it on a new canvas in any editing software.
Align the image on the centre. It must be at the centre.
Then, use a transform tool to move it where you think it fits with the selection mode - if you move at the bottom left for an example, it also moves down in osu!.
Note: You may try doing with "osu-taiko-small", "osu-fruits-small" and "osu-mania-small" if you're planning skinning them.