Best answer by Transparent
Here's a list of commands for the SMETS1 meters. There isn't a command to set or reset the readings.
I don't know whether you are looking at the figures on the meter itself, or on the In-Home Display (IHD). Nor do I (yet) have a Smart Meter myself.
It is quite possible that there are different types of IHD or SmartPhone App which do permit you to reset what they display. But that's quite separate from what the Smart Meter itself does.
A lot of people log in to My OVO or use the OVO App to check the Usage Histogram rather than work with the raw meter readings. Is this what you're looking for?