When you pass the share plugin a URL to share, LinkedIn's crawler visits the URL to attempt to pull data from the page directly (either from OpenGraph tags that are present, or by analyzing DOM elements like , 's, etc.)
If you want to change the content that is shared, you'd either have to modify those local DOM elements to match what you want to share if you are in control of the page yourself, or alternatively, you have to not use the widget and switch sharing via API call or via the URL pattern, both of which let you specify share data and avoid the crawler determining that on your behalf.
Additional documentation on sharing via API and URL can be found here: https://developer.linkedin.com/docs/share-on-linkedin