If you want a temporary solution
Open a command line prompt (cmd) and execute
path
that will show you the actual, current path. Inspect it to see whether the necessary directories are really absent. If they are, execute
path=%path%;directory you want to add;other directory you want to add
The path will be available in the command prompt for as long as it's open. If they are present, reboot the computer, the addition to the path may have been delayed after installation.
The permanent solution
For Win10 but I guess instructions are not very different for other flavors.
Open System properties, find Environment Variables. In the dialog that pops up you will see System Variables, among which you will see Path. Select it, click edit and add the directories you need via the New button. Close all popup boxes and reboot (always a good idea when Windows is stubborn ;-) )