In the Recalls window (Planner\View\Recall Patients) select the correct month in the 'Display recalls up to the end of' window eg Apr 2021 or May 2021.
Select the radio button option 'Non-booked recalls, recall letter not sent'.
Tick 'All Users'
Tick 'Limit results to' and select 3 months.
Click on 'Search'
This will show you all patients who are scheduled to have their recalls during the 3 months up until April or May.
I hope this answers your question, if not then please come back to us.