Create daily push notification using Firebase Cloud Messaging
Push campaigns with Firebase Notifications can be sent now or later (scheduled).
You could probably switch to Firebase Cloud Messaging, use their HTTP API and then build a cron script to trigger your notifications automatically on these days.
Or switch to a more mature product like Parse Server, Batch.com or anything else as they usually provide that daily/weekly/monthly recurring push notifications feature.
Recurring messages are available in FCM now. May be helpful to someone.