It has been a few years since I used the bassinets on United (my son is 19), but basically the bassinet fits into the holes on the wall of the bulkhead, but note the bassinet is not available during take-off and landing. The bassinet is only available during the flight and if there are turbulence you need to pick up your baby and hold them (which is a good thing as you do not want the baby to be a projectile). I believe you need to call in to book the bassinets and as 1K I would assume no charge to call in the request to ensure it is in the system.

I did use the bassinets many times until he was too big - around 8 months or so, and I always placed a blanket over the bassinet to stop the air blowing on him - doctor's advice to limit the direct recirculated air on him.

I totally agree about getting the extra seat if you can. Also, I would still request the bulkhead seats (and as 1Ks this should be doable) so you can place him on the floor when the baby is awake. This gave my son an opportunity to stretch and play, and the space to do this is not available in the other seating areas. But note, you need to put up a barrier if you have the middle seats as people will try and walk on the baby! Not sure why people think it is fine to use the middle seating area of the bulkhead as a walkway.

Business class on United does not have fastenings for bassinets unlike many other airlines. My son flew in business class once he was out of the bassinet stage and it was very easy for him to sleep as the seats are long enough! :-)

(Also, on doctor's advice baby Panadol 20 minutes before take-off and landing to help with the pain of the change in pressure. Yes, I would also feed him but the tubes in their ears are so small and it is the number one reason babies cry on a plane. Just watched a baby throw up on my LHR-LAX flight as they could not cope with the change in the air pressure. I am not a big one for medications but did this until he was about three.)

Happy travelling and make sure you enroll your child in MP. My 19 year old is at 275k lifetime miles and most of the time I used miles for his flights.