Hi! How do I submit more than one photo withou…

Hi! How do I submit more than one photo without sending more than one submission!

I know you can through the app but desktop may not let you? BUT if you want to do this on the desktop, submit your first photo with any caption you want to use and then send the follow up submissions with a note in the caption saying “add this to the other post” or something that lets me know what you want to do and I’ll fix it =)