Create folder in ejabberd installation
mkdir -p ${EJABBERD_HOME}/.ejabberd-modules/sources/ejabberd-contrib/ejabberd-elixir-modules
Put your modules into ejabberd-contrib directory, and run
ejabberdctl modules_update_specs ejabberdctl modules_available
If your modules appear,then let's give a try install your module
ejabberdctl module_install mod_name