If Emacs recognizes the encoding of a file incorrectly, you can reread the file using the correct coding system by typing C-x <RET> r coding-system <RET>. To see what coding system Emacs actually used to decode the file, look at the coding system mnemonic letter near the left edge of the mode line (see Mode Line), or type C-h C <RET>.
You can specify the coding system for a particular file in the file
itself, using the ‘-*-...-*-’ construct at the beginning,
or a local variables list at the end (see File Variables). You do
this by defining a value for the “variable” named coding.
Emacs does not really have a variable coding; instead of
setting a variable, this uses the specified coding system for the
file. For example, ‘-*-mode: C; coding: latin-1;-*-’ specifies
use of the Latin-1 coding system, as well as C mode. When you specify
the coding explicitly in the file, that overrides
file-coding-system-alist.