We do not provide DNS servers for your domains. Most hosting providers provide them free of charge. You can also choose a free service like xname.org.
You can modify the DNS servers of each domain purchased with Youdot at any time. The update is done within minutes after validation. Once the new DNS are published, however, there is still a delay, the time to purge the DNS caches.
As a reminder it is imperative that your DNS configuration is good and have knowledge of the domain otherwise we refuse. This is done in such a way as to guarantee functional DNS. A DIG command allows you to check: https://toolbox.googleapps.com/apps/dig/#NS/