Determine polarity of crystal oscillator
Simple two-pin oscillator crystals don't have a specific polarity (the circuit which drives them does). It doesn't matter how you insert it; it'll work.

Since piezo crystals are electromechanical devices, the shock which caused the component to come loose may also have damaged it internally. If the device doesn't work after soldering it back into place, try getting a new crystal.

You might also want to check whether the solder pads on the PCB are still OK. With this type of damage, the copper pads often "stick" to the component rather than the PCB itself.