How to stop files in a new team getting deleted when deleting the original project/team?

Sorry if the title doesn’t make any sense but i couldn’t figure out a better way to word it.

I had been using the free version of figma for a few years, so every time i worked with a new client i would create a new project in a new team so i could use the free design files. So all my clients are in their own separate team.

However, now ive upgraded to a professional licence and want all my clients in one ‘company’ team and just have each client as their own project. I started moving files to the new team, but whenever i delete the old project/team, where they were originally, the files in the new team get deleted also.

The only solution i can think to stop this is making copies of all the files and only keeping the copies, but this would not be practical as then i would have to reassign permissions to all of the clients and other people i work with, which would be extremely time consuming.

I’d be very grateful if anyone has any other suggestions on how to stop the moved files getting deleted when i delete the old project/team. Thanks.