To connect your ORCiD account to Europe PubMed Central, first select "Search and Link" from the options in the "add works" dropdown in your "works" section:
Then Select "Europe PubMed Central" from the list of options provided
You will be presented with a set of search results for your name. You will likely want to edit that search to include full first name to eliminate false matches:
Any results that are already in your ORCiD account will be highlighted in green and won't be able to be selected, which means duplicate records won't be created in ORCiD. You can go through the list of results, click the button to the left of any publications that belong to you, and then click "Continue" at the top or bottom of the page to send your publications to ORCiD.