A wild thought restore the default build ie some laptops come with a disk to restore to as bought condition that should reload the trial. Of course if you have been installing more programs not the best way so ....
Customer service would also be a good place to ask
It depends on from where you got the account- if its via Dell keep your Dell Tag number, Dell Order number and customer id handy when you call Support.
Other Pre-installed versions you probably will need to furnish the email address you would have used to activate the subscription .