Obtaining extension identifier from Microsoft Edge add-on Web Store:

Lets consider 'adblock' as the extension to be added to the extension repository:

• Go to Microsft add-on web store.
• Search for the extension using the search bar.
• From the URL address bar, select the extension identifier which is located after  "/" as displayed in the image below.

• Copy the identifier and paste it in the Extension Identifier field present in the Extension Repository.