Care worker new user rattled (5)
I believe the answer is:
nurse
'care worker' is the definition.
(I've seen this before)
'new user rattled' is the wordplay.
'new' becomes 'n' (abbreviation as in New Testament NT).
'rattled' indicates anagramming the letters.
'user' is an anagram of 'urse'.
'n'+'urse'='NURSE'
(Other definitions for nurse that I've seen before include "one working in theatre" , "One skilled in caring for the sick" , "Care for the sick" , "Minister to" , "Patient tender" .)