door wont shut quietly
 

my back door wont shut without having to give it a bit of a push at times.It
is a double glazed door the previous owners got put in,there is a tiny lever
which is on a spring or something and if I push it in I can usually shut it
but it is wearing the metal strip on the post,door seems to be hung ok any
suggestions how to fix this.
many thanks if you can help

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