The best way to find your maximum heart rate is riding at full gas, on a turbo, for 8 minutes, at night, in a freezing cold garage, whilst sweating profusely and keeping your cadence above 120rpm.
At least that's the way I did it last night. My first coaching session was more of a 'field test' to work about the zones I need to train in. It feels good to have some saddle time and confidence steady growing again.