Graham asked: "Il doit y avoir la lettre s à la terminaison du mot retourné? vous êtes retournés "

Bonjour Graham !​

​I understand your confusion but here is the explanation: ''vous'' can, as you know, be used both for plural you, and for polite, formal you.
In the second case, it has a singular meaning, as it relates to a single person.

So in le Passé Composé, when you use the formal 'vous', it will agree with the single person it refers to: it was the case here, therefore ''Vous êtes retourné [...]''.

Moreover, in different contexts, you could also encounter the plural versions ''Vous êtes retournés'' or ''Vous êtes retournées'' (for a whole woman group), as well as the feminine version ''Vous êtes retournée''. "
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​You can also have a look at our lesson on agreement with "être" in Le Passé Composé Agreeing past participle with subject's gender and number with (+ être) verbs in the compound past in French (Le Passé Composé)

I hope that's helpful!
À bientôt !