Ignore bird among building blocks (3,2,2)
I believe the answer is:
let it go
'ignore' is the definition.
(thesaurus)
'bird among building blocks' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'among' means one lot of letters goes inside another.
'building blocks' becomes 'lego' (I've seen this before).
'tit' placed into 'lego' is 'LET IT GO'.
(Other definitions for let it go that I've seen before include "Disney tune" , "Excuse something" , "Hit song from Disney's 2013 animated feature film Frozen" , "Refrain from comment" .)