How do you trace family back from DNA?

[HarrysMum]

My DNA has 9% Sweden and Denmark. That seems like enough to be fairly true. How far back do I need to go to find who that came from?

I know my great great grandparents were from Germany, but southern Germany.

I only have 4% from Germany.

5% from Norway and 2% from Baltics.

Not concerned too much with the tiny amounts but interested in the 9%


Also my only English is from the east, mainly Essex. I do have Sussex but that isn’t mentioned.
However the really odd one is my Devon and Cornwall family. I can trace them back to the 1500s, thanks to the British Museum. Ancestry doesn’t mention Devon and Cornwall at all and I doubt it is considered eastern England.