You replaced it (4)
I believe the answer is:
thee
'you' is the definition.
(historical second person pronoun)
'replaced it' is the wordplay.
'replaced' becomes 'the' (I can't explain this - if you can you should give a lot more credence to this answer).
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'the'+'e'='THEE'
Can you help me to learn more?
(Other definitions for thee that I've seen before include "Quaker 'you'" , "'U'" , "You in the olden days" , "You (arch.)" , "Archaic form of 'you'" .)