DIAGNOSIS The internal passive radiators (the oval grills on the ends) have likely become stuck or unseated from the impact, killing the low-frequency response.
FIX Gently press and release the center of each passive radiator (the rubbery material behind the metal grill) with your finger. Listen for a slight 'pop' or click as it reseats. Play a bass-heavy track to test.
IF THAT DIDN'T WORK The driver itself may be damaged. There is no user-serviceable internal repair. Contact JBL support; the speaker has a 1-year warranty against manufacturing defects, but physical damage is typically not covered.
HEADS UP The IP67 rating (dust/water resistance) may be compromised after a significant impact that dislodges the radiators or bends the casing.