Nothing is missing. To adjust these you loosen the pinch bolts on the left crank with a 5mm wrench, use the same 5mm wrench to gently tighten down the large black preload adjusting bolt that's found on the outside of the left crank, and then re-torque the pinch bolts.
This bike appears to be in pretty rusty/unkempt shape. It would be a good idea to at minimum remove and clean/grease the preload bolt because it's aluminum and has a lot of fine threads and they can corrode and/or get sticky and disrupt your torque feel.
Some amount of loosening of this kind of bottom bracket is normal and easy to adjust out. There are many questions here on this. The style you have adjusts exactly the same way as the more common Shimano cranks, which is the sort that will more often be mentioned by name in questions. It's also common for lower-end FSA external bottom brackets like this to be worn out, because they're mediocre quality. You can replace the one you have with a Shimano road BB, which are cheaper and better than their FSA counterparts.