If it is installed, then it sounds like your path is not linked to your /heroku/bin directory (its location depends on where you installed it).
You could probably run a search to find the directory like this
find /usr/local -type d -name 'directory_name' 2> /dev/null where
directory_name is the name of your target directory.
You could change
/usr/local to just
/ and it will search your entire computer but it’s quicker to search in likely places first.
Once you find it’s location, you just have to link it to your path (or you could just execute it via it’s full path name)…
-type d is to search for type directory
2> /dev/null is to filter out permission error messages (if it tries a search where it’s not allowed)