You can find muted messages in Gmail by searching for the message itself, like the sender's email address, text within the message, the subject, etc.
Ị nwere ike ịchọta ozi mkparịta ụka na Gmail site na ịchọ ozi n'onwe ya, dị ka adreesị ozi-e nke onye zitere, ederede n'ime ozi, isiokwu, wdg.