There is no autorouter available directly in Kicad. In the past there was a very rudimentary autorouter but that was removed before the 5.x series. Additionally there used to be a big yellow button which automatically linked to start a session with a free autorouter called Freerouting (https://freerouting.org) which you may see referred to in older documentation.
Freerouting is still available and there are (outdated) instructions on the Freerouting website about how to use it with KiCad. There are also a variety of Freerouting spin-off projects around - all of which with variable support However, to cut a long story short, there are some problems with the legal status and maintainace and support for Freerouting and some usability issues with Java apps in general. The developers did not want to build in obsolescence so removed the big yellow button and hence the direct support for Freerouting. However, the same functionality is available if you choose “Export DSN”, process the file in Freerouting and then import the session file.
Opinions are divided about autorouters - they have a role but are certainly not ‘just press a button and its all done’. There was a good talk at KiCon recently about this subject and how to use them most effectively.
What KiCad does offer is generally considered a more useful feature - a push and shove, interactive router.
This video gives you much more of an idea rather than try to explain it.
