If this is a ~recent domain you should have setup a recovery password when first registering that domain. If you’re using the webadmin for the postinstall, it will ask for the recovery password. Otherwise in CLI you can use the --dyndns-recovery-password option to specify the recovery password
Otherwise you should ask for the recovery of the domain on Nohost domain recovery - Suppression de domaine en nohost.me, noho.st et ynh.fr