PHP PDO Display a single record

Question

Hello. I have a popup system where the client chooses which one will appear on the home. If one is already selected he cannot select another. You have to uncheck the asset and mark what it wants. I want to know how to place a warning message, warning him that you already have an asset.

Follows the code:

$stmt = $PDO->prepare("SELECT * FROM comunicados"); 
$stmt->execute();
$result = $stmt->fetch(PDO::FETCH_OBJ);

if($stmt->rowCount() > 1 ):
    echo "erro";
else:
// codigo se tudo estiver ok
endif;