Practise using eraser he designed (8)
I believe the answer is:
rehearse
'practise' is the definition.
(I know that practise can be written as rehearse)
'eraser he designed' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'eraser'+'he'='eraserhe'
'eraserhe' anagrammed gives 'REHEARSE'.
'using' acts as a link.
(Other definitions for rehearse that I've seen before include "Recite - try out" , "Practice for the performance" , "Practise before performing in public" , "Practise parts" , "Run through (a play)" .)