Pooh’s friend is about right to set off (7)
I believe the answer is:
trigger
'set off' is the definition.
('trigger' can be a synonym of 'set off')
'pooh's friend is about right' is the wordplay.
'pooh's friend' becomes 'tigger' (Winnie the Pooh reference).
'is about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'tigger' placed around 'r' is 'TRIGGER'.
'to' is the link.
(Other definitions for trigger that I've seen before include "Set in motion - say gunfire" , "Roy Rogers' horse" , "One pulled to fire" , "Initiate" , "Part of gun" .)