I got the following answer from the support.
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Managing the Enpass subscription is no different from managing a subscription to any other app on your phone. To change the subscription plan, you can cancel the currently purchased suboptions plan. To do so, have a look at this link.
Now to opt for a new plan you have to wait for the completion of the previous subscription cycle.
Warm regards,
Enpass Support Team | https://discussion.enpass.io/