[phenixbb] Coot add DNA base or mutate DNA base

Hi All, I'm using coot to build DNA, when I click "add residue" to one end of DNA, coot automatically add an "A" base to it, but I'd like to add "G" base, is it a way to mutate the A base to G base, I know coot can mutate amino acid residue, is is a way to mutate DNA residue in coot GUI? Thanks ahead. Xiao