Q: Mileage problem please help!!

Description of Problem: Recently I got my truck worked on by a "macanic" who did basic work on my car, changed fluids, oil, etc. the next day I went to pick up my truck and he said there was a power surge and my mileage is now saying that it's 189,699!! I just got this truck, bought used, a couple months go and when I brought it to the guy they reported that I gave the truck at 12,306, when I asked him to fix this problem he told me since it's a digital dashboard that I have to buy a Bluetooth scanner and find an app that will roll it back to what it is. Do you know any apps I can use to connect to the truck wirelessly? And every scanned that's wireless/Bluetooth doesn't say anything about the odometer? I'm afraid if I don't bring the miles back that my truck will lose value and on top of that, I won't know what my mileage actually will be in no time.

My car has an automatic transmission.