If you share a link 2-3 things show up as preview:
2. Description (should be at least 100 characters long)
3. Social image
You can edit this preview in the site meta of your Umso website.
If you update this description you have to make sure to clear the cache for all services/browsers you want to show the updated description with your link.
Here are some tools to clear the cache for the different services:
You can check your preview with this tool.