Lose track of account in simple form (8)
I believe the answer is:
misplace
'lose track of' is the definition.
'account in simple form' is the wordplay.
'account' becomes 'ac' (abbreviation).
'in' indicates putting letters inside.
'form' indicates anagramming the letters (a different form of the same letters).
'simple' is an anagram of 'misple'.
'ac' inserted inside 'misple' is 'MISPLACE'.
(Other definitions for misplace that I've seen before include "Set in the wrong position" , "Mislay" , "Do bad filing" , "Wrongly put - lose" , "Be unable to find" .)