Hello @Vassilis0,
I'm not certain but that sounds like the email address is already used by another Airbnb member.
To find contact details for Airbnb please type "contact airbnb" in the "Search for anything" search box on this forum. One of the first 3 posts in the search results should have information on how to contact Airbnb.
By "location" if you mean the the pointer on the map you should be able to change this by going to your calendar then selecting the 4 bar icon in the top left.
Then select location and drag the map so the pointer points to your location. If this doesn't work report it to Airbnb.
If you mean the text form of your address like, "2001 Long Drive, My Town" you can't change this. You'll lhave to ask Airbnb to change it.
Steve.