Hey, @Robina –
A 500 attendee Large Meeting add-on will only allow 500 participants, and Meetings can only be upgraded to 1,000 participants. You should consider converting the meeting to a Webinar, and get a large enough capacity Webinar license to meet the needs of all your registrants. Let me know if you need help with this – it’s not difficult.
i highly recommend thoroughly reading this Zoom Support article on Scheduling a meeting with registration, especially the section on Restrict number of registrants.