When I share files ,How can I Know Who it is?

We need to share the files to other company , But only their nickname what i know, how can i know their Email?
thanks,

Hi there. In order to share a file you’ll need to know their email (at least initially). Once you do you’ll then be able to search and add to the file based on their account name.

Thanks Josh’s feedback~
When I have already invited everyone email. On the figma only know everyone nickname. If they change their nickname , I can’t check their email to find who are they.

Can you share a screenshot of where you see this. Is this when sharing a file or managing the team?