How to deal when submitting an extender paper to a journal from another editorial?
That depends on what you mean by "extended". If it just extends the results of the conference presentation, all you have to do is to state this in the introduction and cite the previous paper. If "extended" means longer than the page limit of the journal, it is very probable that it will be rejected outhand or only accepted for further consideration if you cut it down to size. You might try to ask for leniency from the editor, but only after doing a serious effort to make it fit (perhaps by dividing into several?) and have good reasons why it can't be shorter.