How to check if a date within a new date range (from date - to date) already exists in table?

[Metworks_IT]

Hello, I was hoping someone might have some ideas how to approach this problem:

I have an app - Attendance - where Worker logs their annual leave requests and is being processed by Supervisor, so far so good. EG from 12/Apr to 16/Apr, Annual Leave.

Supervisor also adds training dates on behalf of Worker - EG 22/Apr - Training - so Worker would see it on their calendar, gets reminders, etc, all good.

Problem: How do I check if a date in date range is already booked, to give a warning to Worker, if they want to book AL between 21/Apr to 25/Apr, to let them know that they were already booked for training, on 22nd?
And if they really need it, and they proceed, it would trigger an email to Supervisor to re-arrange training, etc.

If Worker would only request a day off, I have that covered, checking if said date is already booked. But just can’t figure it how to check within date ranges.
I have it working after sync, relying on auxiliary tables - currently used by Supervisor to monitor team training date - but I want to get that warning in the form, before Worker submits their AL.

Thank you all!