When I enter your iCloud account on iPhone they show a page in which he said the maximum number of free account used on this iPhone

It's a message that is informing you that you have exceeded the maximum number of free iCloud accounts that you can have on any one device. I believe that the limit is three per device. If you set up other free iCloud accounts or if your phone is second hand and others set up free iCloud accounts on it, there is nothing that you can do about it on that phone. Apple limits it to each specific device. You can create another iCloud account on another iOS device or on a Mac and then use that account on the phone.