How to make a chat based ban script?

The code you have so far will successfully kick the player, but it will not ban them. To ban the player you need to save their UserId to a datastore. This can be done using the SetAsync() method of GlobalDatastore. Below is the code to save their UserId to the datastore.

local ds = game:GetService("DataStoreService"):GetDataStore("Bans") -- Gets the datastore itself so we can add to it.
ds:SetAsync(found.UserId, true) -- Adds the player to the datastore

This can be implemented into your current code like so:

elseif msg:lower():sub(1,4) == ";ban" then
	local  obj = msg:sub(6)
	local found = game.Players:FindFirstChild(obj)
	local ds = game:GetService("DataStoreService"):GetDataStore("Bans")  

	if found then
		ds:SetAsync(found.UserId, true)
		found:Kick("You have been banned!")
	else
		print(obj.." is not a player!"))
	end

But this is not enough to to totally ban the player. To ban the player we're going to need a script that checks if a player is on the Bans datastore everytime a player joins. I recommend putting this script into ServerScriptService to prevent any client access. This script is below.

game:GetService("Players").PlayerAdded:Connect(function(plr)
	local ds = game:GetService("DataStoreService"):GetDataStore("Bans") 
	
	if ds:GetAsync(plr.Userid) then
		plr:Kick()
	end
end)

Let me know if anything is wrong. If my answer helped you, make sure to mark it as correct!