Remove knob from loose pot.
Grab a small crescent wrench.
Unwind any wire wrapped around the pot inside the cavity and push the pot up out of the cavity as far as it will go.
While holding the pot from inside the cavity, tighten the nut on top with the adjustable wrench until you can't turn the pot from inside the cavity.
Test the pot to see that it A) does not spin completely around any more and B) works.
If so, close up the control cavity and put the knob back on.
"Strictly speaking, there is no certainty, there are only people who are certain." -anon-