Quieten down a very quiet facility (7)
I believe the answer is:
appease
'quieten down' is the definition.
'appease' can be an answer for 'quieten' (appeasing is a kind of quietening). I'm not certain of the 'down' bit.
'a very quiet facility' is the wordplay.
'very quiet' becomes 'pp' (musical abbreviation for pianissimo).
'facility' becomes 'ease' (I've seen this in another clue).
'a'+'pp'+'ease'='APPEASE'
Can you help me to learn more?
(Other definitions for appease that I've seen before include "Mollify or calm by making concessions" , "Make peace with" , "Placate by making concessions" , "Calm, pacify, placate" , "Placate by giving in to demands" .)