***Got it!*** I have the original which doesn’t have the outdoor equalizer option. And the manual as you saw doesn’t even offer a clue either! Did you try reviewing the support site? [https://support.ultimateears.com/en/wonderboom2/|WonderBoom 2 FAQ]
All I could find is this question listed in Ultimate Ears (UE) support site:
[quote]***What does the button on the Bottom of the WonderBoom 2 do?***[br]
There's a button on the bottom of the speaker with a little tree on it. Once activated, it ***increases the speaker's overall volume and frequency response***. This mode reduces bass, while upper mids and highs become more present; this allows the speaker to push more sound without distorting (read: it's a lot louder).[/quote]
OK, what happens when you press and hold the indented space? Also try two presses quickly. If the button is not responding then it might be a bad unit. [https://support.ultimateears.com/en/email-support/|UE Support Contact info]