If it doesn’t install the new version, edit the file /usr/local/hestia/install/upgrade/upgrade.conf and replace
rc_v='1.6.8'
by
rc_v='1.6.9'
And execute again v-add-sys-roundcube
Here you have a detailed guide, just change the versions to the current ones and also the admin user (If you are using other administrator user with new Hestia 1.9.x version use it instead of admin).