You can install it directly from the Insomnia Plugin Hub.

Insomnia plugin that provides the ability to run multiple requests in a folder for specifed number of times.

This allows you to easily run all requests in a given folder in sequential or parallel, and see the results (http response code, response time, etc) in a list with a single click and also select or unselect the request using the checkboxes beside the request.

In addition, the plugin validates the response code of each request, and displays a warning if any of the request results do not match the expected response code. To configure the expected response code, add the response code to the request name in brackets, e.g. Get User [200], if no response code is mentioned 200 is default which can be edited in the text field Default status code. If the response code of the request does not match the expected response code from the name, the request will be marked with 'Failed' in the list.

By default the requests in folder are sent once, this can be edited in the text field Loop For

Go to Application -> Preferences -> Plugins and enter insomnia-plugin-run-requests-parallel in the npm package name field and click on the button Install Plugin.

This will download and install the plugin. After installation, you will see the plugin in the list of installed plugins and the action "Run All Requests" will be available in the context menu of a folder, no restart required. (download here)

This is a modified version of Run All Requests by Thorsten Schminkel