>I need to change the data session to the one calle "unknow".

Datasessions don't have names, just numbers. When ever you see a name in the View Window, its the name of the form or Default or something. When its "unknown" it could be that the DE was left around because of Dangling Object references, or the form closed but the data had to stay open because there were still Field Rules or RI or Triggers or Uniquness failing that wouldn't allow you to save.