Flip_peptide [id an atom] or [mol res atom]
This is an easy but dirty way to flip peptides, since the peptide group simply is rotated 180 degrees around the CA -- CA direction. After the flip, the geometry of the peptide group of the current and adjacent residues are slightly distorted. The operation should therefore be followed by a regularization or a database fragment fit. This is an immediate action command, there is no need to accept/reject the new coordinates. If you regret the flip, simply activate the command once more.
You must identify any atom in the residue whose carbonyl oxygen gets flipped. A number of people have identified the nitrogen atom N of the next residue, thinking that will define the peptide. They are surprised to see the `next' oxygen flip!