The executable of WSL is C:WindowsSystem32wsl.exe. You can just type wsl in Windows Command prompt and you will be logged-in to the default WSL instance. Or type wsl -h in order to get the list of all available options. In batch files you can use:

C:WindowsSystem32wsl.exe <your script or command>

Or if you need to run the command as root:

C:WindowsSystem32wsl.exe sudo <your script or command>

Probably more correct way is to use wsl -e -- <command>, but the above works nice for me. Here is more detailed example: Ubuntu 18.04 on WSL cron daemon not running after reboot.