Best bet is to perform a ramp test to get your max HR as a starting point. Depending on where you live it can be done in a few different ways.
My preferred way would be to ride to long, steady gradient climb, including a very good warm up. Then when at the climb ride hard for 5 mins, then every 30 seconds change up a gear(accelerating to maintain your preferred cadence) until you feel you cannot sustain the new gear for the full 30 seconds then sprint flat out for another 30 seconds.
Beware this will hurt like hell and it could be best to have a friend on hand in case you black out
If you live in a flatter area, do as much of the building phase on the flat then hit a climb absolutely full gas.
The zones given to you by Strava seem waaay out unless your mas HR is very very low, which it could be for a variety of reasons but I would be surprised if they proved to be accurate when compared to your actual max HR.