Once a form has been created, the table it is using (i.e. where it saves submitted records, or where it edits records from) can no longer be changed, since each table has its own unique references for fields etc.
If you need a form in a another table, you'd need to create a new form.
You can see which table your form is linked to (i.e. which table the records will be saved in) under Form Table in the Table & Login section. This contains a direct link to your table for your convenience.