Hello.
Boolean controls can only have 2 possible values, true or false, and there is no way to add more values to them.
If you need more values, then you must use a numeric control (or a string, but I tend to like numerics better, although strings could be just as useful).
There are several types of numeric controls you could use to provide 3 or more options. Attached is a VI which shows a ring, a knob, and a slide each with 3 possible values. In your code, you would then perform different actions depending on the numeric value of your control.
Hope this helps,
Alejandro