How can I check on a flight scheduled for July to see if there are any available seats on that particular flight? I have the flight number.

Check with your individual airline

Normally that service is available from the airline's app.

Go to the airline website. You will need last name and record locator

Would suggest calling the specific airline carrier. Or using one of the booking agencies such as Priceline. When I took my flight got numerous reminders that bookings could change. I know Delta only books st 60 percent capacity and was extremely safe