How i can set max grow on Player? My script not work...

It would seem that you reset your debounce inside the elseif section. Debounce should be reset outside the if elseif else end section.

replicatedStorage.Simulator.Test.OnServerEvent:Connect(function(player)

    if not remoteData:FindFirstChild(player.Name) then return "NoFolder" end

    local debounce = remoteData[player.Name].Debounce

    if not debounce.Value then

        debounce.Value = true

        if player.leaderstats.Power.Value < 3000 then

            player.leaderstats.Power.Value = player.leaderstats.Power.Value + 1 * (player.leaderstats.Rebirths.Value + 1)

            player.leaderstats.Money.Value = player.leaderstats.Money.Value + math.random(1,4) * (player.leaderstats.Rebirths.Value + 1)

        elseif player.leaderstats.Power.Value >= 3000 then

            player.leaderstats.Power.Value = player.leaderstats.Power.Value + 0 --this line is not necessary, but you may want to leave it for clarity

            player.leaderstats.Money.Value = player.leaderstats.Money.Value + math.random(1,4) * (player.leaderstats.Rebirths.Value + 1)

        else --this else is not needed

        end

        --move this two lines
        wait(cooldown)
            debounce.Value = false

    end

end)

Have a nice scripting session!