OBS Multi-Stream Plugin - Multi RMTP Plugin

https://obsproject.com/forum/resources/multiple-rtmp-outputs-plugin.964/

This plugin will allow you to duplicate your stream across multiple platforms.

You only want to add the "extra" platforms to the plugin settings as your normal OBS "Start Streaming" button will stream to your current main platform.

So if you are streaming to twitch, and you want to add KICK, you just add KICK to the plugin, and when you hit start streaming in OBS you will go live on twitch. You can either set the plugin to start streaming with OBS, by checking the box, or you can manually start the stream to other platforms with the buttons.