Need help for X automated answers and DM

Does anyone know a tool that can automatically reply in DMs? I tried Make but don’t have the DM option, and Zapier doesn’t seem to support it either.
I specifically need an automation where:

When someone replies to a post with a keyword, they automatically receive a DM.
After that, I also reply to their comment saying the message has been sent.

Any suggestions or hacks to make this work?

Usually you'd go for panels for that sort of thing. That or have a custom tool coded to do just that, should be fairly straight forward.