Issue with site subsite creation

Hello,
I am having issues creating subsites. with prosites? i don't see the site being acknowledged to be created;
Wen adim add a new site , I have this message :
<h1>Déjà installé</h1><p>Il semblerait que WordPress soit déjà installé. Pour le réinstaller, commencez par supprimer vos anciennes tables de la base de données.</p></body></html>
whic means WordPress is already installed.

in my error window in wpengine, I have a lot of errors... tried to r restore an older version biut but seems buggy still. what should i do ?

BEST REGARDS,
Herve