Reconnect the SharePoint site of a private channel back to the Files tab of that private channel

Franck1304Unfortunately not, the easy solution of workaround for this use case will be blown steps;

1. Create a new private channel with a slightly different name and add the members
2. once the channel is created click on files click go to SharePoint so the child site is open
3. from the old child site that you have screenshot move or copy the files to the new channel site
4. Delete the old channel as it will delete its child site created with that.

you maybe have different options in mind but this is just a quick workaround.