Hi Radu,

Welcome to the Box Community, I'm happy to help!

If you've accidentally removed your access to a collaborative folder, in order to gain access again, you will need to reach out to the owner or the person who shared it to you and request that they re-invite you to the folder again.

To learn more about inviting collaborators in Box, please take a look at this article: Inviting Collaborators

Thanks for posting and let us know how else we can help!

Regards,