Turn up: no seats upstairs, so go back to where you were (4,4,6)
I believe the answer is:
come full circle
'go back to where you were' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'turn up no seats upstairs' is the wordplay.
'turn up' becomes 'come' (both can mean to arrive).
'no seats upstairs' becomes 'full circle' (I've seen this before).
'come'+'fullcircle'='COME FULL CIRCLE'
'so' acts as a link.
Can you help me to learn more?
(Another definition for come full circle that I've seen is " go back to start".)