How do I make the game sends you notifications to your devices when you are not playing it?

How do I make the game sends you reminder notifications to your devices when you are not playing it?

If so, how can you set a "periodicity"?

There is a Mobile Notifications plugin in the Construct Master Collection.

chadorixd.itch.io/construct-master-collection

You can use OneSignal, it works great and is very easy to use. You can use chadoris plugin, or you can just use it without any plugin, since it is very easy javascript (but then you need to build the app via other builder than C3 export)