For those who setup Ubuntu Linux Bash on Windows 10 but forgot what password they used. I set this up quite a while ago on a computer that I seldom use, and I needed to reset my password. Here are the steps I found from Ask Ubuntu.
bashand make a note of your Linux username (this need not match your Windows username)
In Windows admin command prompt (Super+X, A) change the default user to root:
lxrun /setdefaultuser root
Now Bash on Ubuntu on Windows logs you in as root without asking password
passwdcommand in Bash to change the user password:
Change the default user back to your normal user in Windows command prompt
lxrun /setdefaultuser your_username
Where are my Ubuntu Bash files in Windows 10?
In Ubuntu Userspace for Windows, the Ubuntu file system root directory is at
Replace the Username with your Username on Windows.
The Ubuntu system files are stored at:
Your Ubuntu user account’s home folder is stored at:
The root account’s home folder is stored at: