Did you installed it? If yes then check and make sure your installed version is compatible with your SW version.
If nothing works then contact CustomTools tech team (they are very speedy/helpful in responding)
Further to Deepak comments, have you also activated the customtools add-in?
CustomTools will work up to 3 older versions of SW installed as well FYI. Eg CustomTools 2017 will work from 2014 upwards.