You can only cancel nursery requests that have not been paid, meaning for future months. If this is the case, from the benefits tab, by entering the nursery benefit, you will be able to see the requests you have active for the upcoming months.
Next to each request, you can view its details and a red bin icon which you can use to cancel it:
Once you have done this, you will receive an automatic email confirming the cancellation of the request, and you will no longer see it active in your app.