You can't. They only depart from Union Station or Van Nuys.
Take the Metro Gold Line from Glendale to Union Station then walk over to the bus terminal to catch the Flyaway from Bay #1.
The Flyaway only departs from Van Nuys or Union Station but if you can find a train ride to Union Station and check the schedule for the Fly away, you can easily grab the bus right after you get to Union Station.
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