Ducati Monster 620 Owner's Manual page 121

Note
Never touch the transparent body of the new bulb
with your fingers or it will blacken resulting in reduced
bulb brilliancy.
Insert the locating pegs of the bulb base into their seats
to obtain correct alignment; hook the clip (3) to the
headlamp holders.
Reconnect the cables.
To change the parking light bulb, withdraw the bulb
holder (4, fig. 35). The bulb is of the bayonet-type: press
and rotate anti-clockwise to remove. Fit the spare bulb by
pressing and turning clockwise until it clicks Fit the bulb
holder again and assemble the rim-reflector assembly.
E
fig. 35
49