Currently appointment scheduled but eligible for dropbox

I currently have a scheduled appointment for October 2022 for my parents tourist visa renewal.
They have their B1/B2 visa expired in June 2018
In that case they fall under dropbox eligibility of 48months extended.
But since they already are scheduled for inperson interview on CGI… it is now not showing any dropbox appointments for them.
How can I look for dropbox in this case where they were already scheduled for in person previously.
Please help me on this. Looking to get their stamping from 2020