Currently there is no zoom option on Average Waveform Graph and other graphs. Time axis is fixed on +-2ms.
Another option would be to play recording and use Threshold Mode to get average waveform of 50 EMG spikes. Please refer to our manual for details in Thresholding section:
https://backyardbrains.com/products/files/SpikeRecorderDocumentation.2018.02.pdf
If you would like to do offline analysis and get average waveform for whole recording you will have to load signal file (.wav file) in Python, Matlab or some other tool where you can write custom analysis.