You’ll need to expose an endpoint of an intermediary server and make some kind of a database. Roblox doesn’t have any viable way of running a single script for an entire universe, so everything will have to be handled by the bot.
Bans are easy to make. Send a request when a player joins, check if they are marked as banned in the database and return that value.
Kicks are a bit trickier, but should be possible with a hacky solution.
You can set up a server and send requests to it. For a ban system, you can store the banned users in a database on your server. For kicking, you can keep sending requests to your server until the server indicates that there is an update.