Monsieur Dupont, vous vous êtes trompé.
Why do you use être here instead of avoir. Shouldn't it be 'avez'?
Reflexive verbs like 'se tromper' are conjugated with 'être' without exception in the passé composé.
Here is the link to what constitutes a reflexive verb for your perusal -
Take a look also at the following Kwiziq lesson on the subject in question -
Hope this helps!
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