The V3R doesn't remember it's settings - to be on the safe side you have to do a quick wetup every time you switch on.
To reset the speedo, switch off and unplug the batteries.
Then, with your transmitter on, plug in the batteries and switch on the speedo.
The FIRST thing you should always do when switching on is to go to full forward throttle. The SECOND thing you should always do is go to full reverse.
The speedo is now set.
In theory, it should remember these settings, but it can't be relied upon - you do need to make sure you use full forward power FIRST. Never use reverse directly after switching the speed controller on, it will mess up the settings.
If it nothing works at all, it could be a damaged speed controller.