How would I make a ban list for this ban script I have made?

Make a table containing the players you don't want to be in your game.

local bans = {123213213,49494932} -- ids


game.Players.PlayerAdded:Connect(function(plr)
    for i,v in pairs(bans) do
        if plr.UserId == v then
            plr:Kick("ha get rekt skrub")
        end
    end

Tables and Modules

To better store our information, we can use a table or module script containing a banned player's user id. For this example, we will use a table. A table can be used to store values, we will store our banned player's UserIds in there.

Why their IDs? That way they will remain banned if they change their name.

To loop through the banned player list, we will use X,Y in pairs. pairs are commonly used to filter through a table of objects or values. In this situation, it will loop through a table of player's user ids.

Example of pairs:

for i,v in pairs(game.Workspace:GetChildren()) do -- this will run and collect information about the workspace's children
    print(i) -- the first value (i) is the number of objects/values it collected. 
    print(v.Name) -- the second value (v) is the actual object/value itself. This case, we will have to print the name.
end

Solution

local BannedPlayers = { -- start of table
    0, 
    1
}

game.Players.PlayerAdded:Connect(function(plr)
    for _,banned  in pairs(BannedPlayers) do
        if banned == plr.UserId then
            plr:Kick("Hi you are banned")
        end
    end
end)