To install NeoMutt into your profile, run
guix package --install neomutt
To upgrade just NeoMutt in your profile, run
guix package --upgrade neomutt
To remove NeoMutt from your profile, run
guix package --remove neomutt
To build NeoMutt from the HEAD of the NeoMutt sources, you can use the
contrib/guix-neomutt.scm file with any of the relevant guix
commands. For
example
cd contrib
guix package --install-from-file=contrib/guix-neomutt.scm
for installation,
guix build --install-from-file=contrib/guix-neomutt.scm
for building it.
Read the GNU Guix Reference Manual for more information and examples on usage.