Don't try to find your max HR. Instead, ride up as long a hill as you can find and push hard until you start to pant uncontrollably. Hold that for a bit, then back off until you stop panting and are just breathing deeply and fast. Use the HR you can hold there as your lactate threshold heart rate (LTHR) until you can get more experience and establish it more accurately. But that will do for now. Then base your zones of your LTHR:
Joe Friel's Quick Guide to Setting Zones | TrainingPeaks