On your Jira Cloud instance navigate to the homepage by clicking on the Jira Logo.
Then click the cog icon to navigate to the Jira settings admin page.
Scroll down to find the section Atlassian Marketplace and click on Find new apps. On the marketplace, search bar look for External Share for Jira
This is the direct link for the marketplace: (Change <YOUR_JIRA_URL> to your Jira URL)
https://<YOUR_JIRA_URL>.atlassian.net/plugins/servlet/ac/com.atlassian.jira.emcee/discover?s=com.atlassian.jira.emcee__discover#!/discover/search?query=External%20Share%20for%20Jira