You can set up Rolling Contracts when you create a new Licence. Alternatively, you can edit an existing licence (using the pencil next to it) and enable this option. 

On the licence detail page, in Editing Mode, you will find the Licence Term section. Here is where you can check the Is Contract Rolling? box. 

In such a case, your contract ends whenever one of the agreeing parties decides to end it and not on a specific date. 

Instead of an End Date, it is necessary to add the date when the Licence will be reviewed. 

Once you have set this up, simply continue configuring your licence as described in the guide.