Senate elections are held every fall on the second consecutive Wednesday and Thursday of classes in October. For 2019 that is October 9 and 10.
The Senate filing period begins on the 6th CSUN business day in September and closes 10 CSUN business days later. For 2019 that is September 10-24.
Additionally, you can email firstname.lastname@example.org for information about legislative internships which do not require running in an election.