DNS can make your internet feel faster by reducing the time it takes to start loading websites or YouTube videos, but it does not actually increase your download or upload speed.
Most ISPs use default DNS servers, which are often slow or overloaded. I didn’t realize that every time I opened YouTube, my phone first had to ask the DNS server where youtube.com is located. You can check out more details here: https://gsmrumors.com/i-changed-this-dns-setting-and-youtube-feels-faster/