Copy de Databse to your pc
( make a backup of the database )
Use SQLLite Expert Personal to edit the database
Go to "Device Status" and look for the row on the right side with your device
Double click on the row, goto "SValue", edit this, click ok, clock ok again.
Then the most important one:
On the leftside goto "MySensorsVars", click on it, on the right side you will see your MySensors devices, click on your device and edit the "Value"
Both SValue and Value should be the same and match whatever your whatever meter reads when you start using your sensor.