I think this is just being overcomplicated. You simply go to where you registered your domain (ovh.com) and register the the nameservers they gave you, to the IPs they gave you. Most domain registrars provide a way of doing this using their interface, some require you to contact them.
Your server management company just wants you to have the:
ns1 = 91.121.126.84
ns2 = 91.121.127.84
Once that is done, you can use those as nameservers for your domains, which will point the DNS to your new server.