Alright, so here's what you'll need to do. This is unrelated to TruckersMP, but I'll help you anyway.
Go to your documents, then open up the Euro Truck Simulator 2 map. There should be a map called; "Profiles". This is the part you want to keep in mind.
I really hope you still have access to the old ETS2 folder, as that is where it will be stored. If you do not have a copy of your previous profile, you will not be able to retreive your old account unfortunately (Mods, correct me if I am wrong).
If you do not have access anymore, then, unfortunately, you'll have to do everything all over again.