Fallout 76: Bring the Key Fragments to Rose - Key to the Past

Bring the Key Fragments to Rose is an objective in Fallout 76 (F76).

Quest

With the final Key fragment collected form David Thorpe, it is time to return to the Top of the World.
Go inside, up the to the Observation Level, over to the left, through the door.
Once again, talk with Rose.
- It make take a few initiations for Rose to actually take the key fragments.
Apparently though, there is one more thing you will need to do to unlock the cache that Rose is after.
Looks like you will need to head to Charleston.