Problem with PiwikTracker during creating fake data

Good evening…I am Ioanna and I have the following question.
I have locally install the demo release of matomo.
I would like to create fake date. While I try to create a website with the comand
visitorgenerator:generate_websites --limit 2
For examlpe the system response that
0 websites are generated
Although when I check matomo there is a new site build.
When I try to create visits with the visitorgenerator command I receive this message

You must first set the Piwik Tracker URL by calling
PiwikTracer:: $URL=';

The matomo site gives the following advice to add
small part of code in the webpages html file.
The problem is that I can not find anywher in my files
this file. So I cant fix the problem. Please help me.
Thanks in advance…