I am afraid it is not possible to archive patients on mass. You will need to do it one by one. If you think this would be a good idea for the development team to add in the future, please make a post on the ideas page: https://community.carestreamdental.com/t5/PRODUCT-IDEAS/idb-p/practicemanagementideas
Just to add to Liam's post.
Whilst it isn't possible for a site to bulk archive patients it is something that the helpdesk can do.
Please could you call 0330 094 8194 option 1 and we will discuss this with you.