The standalone should come with psychtoolbox included, but this may depend on the version of psychopy you are running. One thing is, this message is really just a warning (but your keyboard should still work There is a problem after running experiment: No module named 'psychtoolbox')
Please could you share with us some details on:
what version of psychopy you are running
what operating system you are on
If you open your programme files C:\Program Files\PsychoPy3\Lib\site-packages do you find a folder called “psychtoolbox” in there?
For context, please could you let us know whether this is an experiment you will eventually take online (in which case an easier solution could be to track a mouse release if you are tracking the release of a single button 
Thanks,
Becca