This would be better if posted in the Apple Devices forum. Perhaps one of the moderators can relocate this thread for you.

I recently updated my iPhone 6 Plus and iPad Mini 2 Retina to iOS 10.x.x. However, I had no future reminders at the time. So I cannot help you out. My guess is that the only way you could get them back would be if you had backed up the iPhone before you ran the update. Then you could restore data from backup. I have no clue whether Reminders are backed up though. I do assume you are talking about Reminders that you setup in the Reminders app. I do have recurring Calendar events that I setup, and they all seem to have been retained during the updates.