Talk up erstwhile turn of fate (5)
I believe the answer is:
Here is my best explanation:
'talk up' is the definition.
(I've seen this before)
'erstwhile turn of fate' is the subsidiary indication.
'erstwhile' becomes 'ex'.
'turn of' shows that the letters should be reversed in order (I've seen 'turn' mean this).
'fate' becomes 'lot' ('lot' can be a synonym of 'fate').
'lot' back-to-front is 'tol'.
(Other definitions for extol that I've seen before include "Praise greatly", "Applaud", "Warmly approve of", "Praise - honour", "Commend", "Enthusiastically praise", "Highly rate", "Talk up", "Proclaim" and "Say great things about".)