The String's Value won't change to Player's Name?

Hello. The problem is that you used an in pairs loop which would run before the touched event fires which would mean the loop wouldn't find anything in the table so it would go on with the rest of the script. Instead, use a coroutine with a while true do loop which checks if a player is in the "playersIn" table. Also, I used a connection variable with :Disconnect() to prevent other players getting added to the table. Try this:

local playersIn = {}

local string1 = workspace.player1

local connection 

local function onTouched(hit)
    if hit.Parent:FindFirstChild("Humanoid") then
        local player = game:GetService("Players"):GetPlayerFromCharacter(hit.Parent)
        table.insert(playersIn, player)
        connection:Disconnect()
    end
end

connection = workspace.red.Touched:Connect(onTouched)


coroutine.wrap(function()
	while true do
		if playersIn[1] then
			string1.Value = playersIn[1].Name
		end

		wait()
	end
end)()

Coroutines are a way to use code without yielding the rest of the script. Please upvote and accept this answer if it helped.