[Chimera-users] Nucleotide Mutagenesis in Chimera

Hello, I am trying to mutate nucleotide residues in RNA using Chimera, and I've seen previous posts about using the "swapna" command. However, Chimera is giving the error message "Unrecognized command: swapna". Is there a way for me to enable swapna for Chimera to recognize so that I may use it? Thank you, Shaimae