With this plugin you can copy the content of an entry to another site.
composer require goldinteractive/craft3-sitecopy
When editing an entry at the bottom of the right panel you will find a toggle to enable site syncing. From there select the site that you want to overwrite with the currently visible content and then just save the entry like normal. Any content of the current site will be automatically copied to the selected site.
Attention: This action will OVERWRITE all content from the selected site.