You have to manually locate yourself on the map every time. Since a desktop PC is generally in a fixed location, I suggest finding where you are on the map and saving it as a favorite. You'll also want to make sure you save it as one of your places in Cortana.
There is no way to manually set your actual location in Windows 10. Microsoft is smarter than you. If they say you are 70 miles away from where you think you are, then that's where you are.
I actually go into Bing and reset my location manually as a city in Mississippi, but every time I restart my browser or restart my computer, it resets me to Atlanta, Georgia every time. I'm 295 miles away from there. Still, I must be in Atlanta, since Cortana tells me so.
I have a USB Dongle that is a GPS Receiver. If I plug it into my computer, I get an accurate location every time. I shouldn't have to do that. It's a laptop, and I'm not always docked. If I dock on my desk in the office, it accesses the GPS receiver on the USB Hub. If I'm on my dining room table in the same house, I don't have the GPS receiver, and suddenly I've traveled nearly 300 miles in under a minute. :shocked:
All I can say is, I feel your pain. This is something we need to voice to Microsoft via Uservoice.