Vw Lupo 3l Automatic

Hello friends.. I got a Lupo a few days ago. Suddenly it makes me problem. 5speed.as soon as it changes to 5 it does not accept any gas, must always restart. Error message G38 gear speed implausible signal sporadic. I was told that the gearbox renewed the basic setting execution needed. Vcds I have, unfortunately I lack the instructions to perform this.