If you want to have new users of your product getting a Trial License by themselves, you must Allow Trial for this product.

Then you can follow this procedure to configure the default attributes and settings for the trial licenses auto-registered.

Select in the tree the product for which you want to set the Trial License Settings,and click on Open LabVIEW Project.

Locate the Startup VI for your application. This VI must be named with the name of the product followed by "_STARTUP_VI"

Open this VI and displays its Block Diagram.

Locate the Trial License settings cluster and adjust the license settings as you want.
See the LabVIEW Context help for the cluster for more details and see below for more information on the various attributes:

oAllowOfflineTrial: By default, it is possible to request a Trial License using the Offline Activation process. However, you can prevent this by setting this attribute to False.

oSkip Existing License Check: By default, it is not permitted to request a new License using an email address that is already associated with an existing registered License. Setting this attribute to True allow to bypass this rule and allow someone to get a new License with his email address, even if he already has other License(s) with that same email address.

oAll other attributes are described on this page

Save and close your VI. You can Build and Distribute your product.