If you don't have the license owner's info any longer then do you know anyone with entitlement to open a support case? If not then it's like putting your system's root password into a safe and then losing the safe. Things become a lot harder.
Contact your Splunk account team for assistance. They can work with Support to assign a new license owner. They may even be able to get a license reset key for you.
--- If this reply helps you, Karma would be appreciated.