On matrix2, you can type the alliance keyword two ways:

#1: In the "Departing from"/"Destination" boxes directly.

Example:
Departing from: BOS::/alliance star-alliance

spaces are not significant (except after "alliance"), but you must have the "::" before the "/"

#2: In the "Advanced Routing Codes" box
Example:
Departing from: BOS
/ alliance star-alliance

in this case you don't need the "::", and spaces are still not significant.

If the above don't work for you, please send me a PM with details about your computer and browser.