Remove the battery and tip the mower so the right side wheel is facing upward. Beware of the blades as they are sharp and can turn suddenly. Never work on the mower while the battery is fitted.
Using some small pliers or a circlip remover spread the sides of the circlip so it can clear the slot in the end of the axle. It is possible but fiddly to do this with small screwdrivers but take care as the clip may spring away.
Remove the clip and the large washer then lift the wheel off.
Inside the wheel you should see this gear assembly with a Drive Belt.
The Drive Belt should be a single loop around the blue circled small gear on the left of the image below and the larger gear in the centre.
If the belt is twisted, worn on one side or clearly damaged it may be causing extra load on the motor which would result in the electronic overload being triggered and the light flashing on the mower.
To refit the belt remove all the 6 screws circled in red to take the top plate off the large white cog.
Then loop the belt over the smaller cog circled in blue, engage the belt into one side of the large white cog and rotate it while pressing the belt into place from the side.
Make sure it is all the way on and the teeth are engaged then fit the plate back on. Make sure all the screws are tight.