Fix an incorrect default keyboard layout after upgrade to macOS Sierra Public Beta 2

Today I have upgraded to Public Beta 2 as Mac advised, but soon the problems occurred after reboot.

The external keyboard( Cheery G80-3000) failed to work seemlessly with the new system. The key "a" was gone, "H" became "g", "I" became "H", althouth the rest were correct.

It made me frustrated because I have mountains of resumes to work on.

after 3 hours of searching, trying ,testing ,calling the apple care staff..., I have solved it by myself.

The following is my way to success.

(keep your external keyboard connected)System Preferences>key board>change the keyboard type
select another keyboard type other than the orginal. For me, I choose the ISO other than the American
medifier keys> select the keyborad you connected and make some changes.
Then, the miss A comes back, H and I recovered.
I feel I am GENIUS.