API from Rocket.chat

I want to know how i can see a User ID for the API Communication from Rocketchat
And how can i create an accsess Token?

We use PRTG-Networkmonitor for monitoring our IT-Systems. And i want that warnings come from PRTG to Rocketchat over API-Communication.

https://docs.rocket.chat/api/rest-api/methods/chat/postmessage

on this page is explaind how i configure the Api but not how i create a token ore how i see a User ID.