Just go on a subscription payment and toggle it to repeating and the select the interval It often does this automatically but if its not showing up under your committed spends for the next month in Summary, you just need to pop in to a previous transaction and set it up. It’s likely it will already be doing it though in your committed spending!
Edit: My guess is you havnt had a payment yet from these go out of your account which is why it’s not showing up yet in the scheduled payments section. As they’re subscriptions and not direct debits Monzo can’t see them until they come out, but then it normally auto sets them as recurring when they are subscriptions. I think the other people in this thread are getting confused with the bill pots feature which doesn’t sound like what you’re asking for