Open Git Bash. Change to the root directory of Git Bash.
cd ~
echo $PATH
/bin:/c/Program Files (x86)/Google/Cloud SDK/google-cloud-sdk/bin
Edit .bash_profile or .bashrc. It was .bash_profile in my case. Showing a truncated path.
Add your custom path to the PATH variable. Save file. Exit Git Bash.
PATH="/bin:/c/Program Files (x86)/Google/Cloud SDK/google-cloud-sdk/bin:/c/custom/path"
Open Git Bash again and check your updated Path.
echo $PATH
Result.
/bin:/c/Program Files (x86)/Google/Cloud SDK/google-cloud-sdk/bin:/c/custom/path