I noticed under say it there is a open flight plan option how dose this work could not find it in the manual

i had a saved vfr flight plan from EGLC to EGOC i asked it to load the flight plan both with speech and say it+ both times is told me i had no flight plan registared

i was using FS2020 if that makes a difference 

You use the Open Flight Plan phrase with FSS to open a VFR flight plan that has been Filed.  You must have a filed VFR flight plan to use this phrase.

Normally, you would only open the flight plan if you are flying VFR without VFR Flight Following.  You would do this after you are released from Tower or after you are out of the Airport airspace if flying from an uncontrolled field.

Dave