Hi!
First of all I would like to recommend you to change the hook name to the one with using underscore instead of hyphen:
{hook name=“block_description:description”}
If you have already created the override for the mentioned template, then the path should the following:
design/themes/[THEME_NAME]/templates/addons/[ADDON_NAME]/hooks/block_description/description.[pre|post|override].tpl
In case the override has not been made yet, create it at the following path:
themes/[THEME_NAME]/templates/addons/[ADDON_NAME]/overrides/blocks/product_tabs/description.tpl/description.tpl