zgen doesn't do automatic updates like oh-my-zsh. Set up easy auto updating, both of zgen and the bundles loaded in your configuration.
Activate with zgen load unixorn/autoupdate-zgen and regenerate your init.zsh file.
set ZGEN_PLUGIN_UPDATE_DAYS before calling the bundle if you don't want the default value of 7 days.
set ZGEN_SYSTEM_UPDATE_DAYS before calling the bundle if you don't want the default value of 7 days.