Mass bot DM Discord

I'm looking for an application or website that allows me to send bulk messages on Discord (such as a mass bot). Some people offer this service, but they don't disclose how they do it. Instead of paying more money for this service, I would like to learn how to do it myself. Is there anyone who can help me with this?

I can help you as a software developer.
https://t.me/hkeydesign