You need to use the console. (F12 in Firefox and probably also in other browsers)
Use the Code
SugarCube.State.active.variables
to see the variables. After finding out, how they named in the code, you can Change them there.
As an example, with:
SugarCube.State.active.variables.xxx = 10(put variable name instead of xxx)
You change the chosen variable to a value of 10