No endpoints for refreshing linkedin OAuth2.0 Tokens have been mentioned anywhere in their documentation yet. All they say is:
Provided that the user is already logged into LinkedIn, this flow provides you with a simple way of obtaining a valid OAuth 2.0 access token without forcing your user to authorize your application again
But having user logged into LinkedIn wont really solve the purpose of refreshing tokens in backend. OAuth1.0 does have a mechanism mentioned.
One useful discussion on this topic I found : here