If you are unable to locate CM Mobile in the Play Store, this is likely due to the country settings on your Play Store account. Your account must be set to the United Kingdom to install the app.
To change your country settings:
On your Android device, open the Google Play Store app.
Tap the profile icon in the top right.
Tap Settings > General > Account and device preferences > Country and profiles.
Tap the country you want to add an account for.
Follow the on-screen instructions to add a payment method for that country.