Change softkeys on “Today” screen
HKCU\Software\Microsoft\Today\keys\112 — left
HKCU\Software\Microsoft\Today\keys\113 — right
You may not have a 113, but you can just make the 113 identical to 112 and change the “open” command. The value for “Default” controls what is displayed on the screen.
Or if you are not comfortable changing your registry or dont have the tools, then download this free app called Advanced Config
here as it will let you do many things including changing your soft keys by selecting what app you want to use (from a drop down box)