shortcode – Multiple values ​​for a variable

I have a custom plugin written by someone and no longer available.
There is a search option that creates a table of seminars in different cities.

At the moment I can have a query with this shortcode:

[kurssuche class="course_search" place="1"]

That shows a table with all seminars in the city "1". How can I create a spreadsheet that shows seminars for two or more cities?

I am new to this area, every help is greatly appreciated!

This is the code:

                if (isset ($ _ REQUEST['search']) || $ atts['place']! = & # 39; & # 39;
{
if (isset ($ _ REQUEST['city']) && $ _REQUEST['city'])
{
$ where[] = "city = & # 39;". $ _ INQUIRY['city'], "& # 39;";
}
otherwise if ($ atts['place'] && $ _REQUEST['city']! == & # 39; 0 & # 39;
{
$ where[] = "city = & # 39;". $ atts['place'], "& # 39;";
}

$ courseplanList = $ wpdb-> get_results ($ query);
}
}