You start by doing a few Google searches.
http://howtomendit.com/answers.php?id=312923
http://www.peugeotforums.com/forums/307-38/bonnet-latch-31625/
(Actually, you may do better posting in dedicated Peugeot forums)
http://www.peugeotcentral.co.uk/forum-8.html (You need to register to use search)
XXX, December 2016