At the moment, we don’t currently have a great solution for this. It can be potentially achieved through the user of user meta in our User Management addon, but without knowing more about your use case it’s hard to say for sure.
Because we only check these forums once per week, we strongly encourage you to reach out to us here with any followup questions in order to get a timely response: https://ninjaforms.com/contact/ There, we offer support free support directly to our Ninja Forms users with significantly more privacy and a faster response time.