[texworks] Changing the encoding of an already-open file

[Philip Taylor]

In TeXworks, under Edit/Preferences, I can change the default encoding from UTF-8 to (e.g.,) ISO-8859-1, but there is a warning :

/Note:  /These are default settings.  Changes to them will not affect windows that are already open.  Use the respective items in the "Format" menu to achieve that.

What, please, is "the respective item in the 'Format' menu" by which to change the perceived encoding of a document already open in a TeXworks window ?

Philip Taylor