After a 30-day trial period, most software vendors require you to purchase a license or remove their product. In many cases, the features will be disabled so the software is not much use in keeping. I'm not aware of any way to legally reset a trial period. If you encountered an issue before the trial expired and were not able to use the anti-virus then you need to contact Kaspersky Lab Support
If the trial period has expired and you just want to reset it in order to continue using, then we cannot offer assistance that would circumvent the procedures a software vendor has implemented in offering a free trial to users.