1. On the Engage Sales Tool tab in Salesforce, click on 'Engage for Gmail'. Contact your admin in case you don’t seem to have this tab.
2. In order to open Chrome’s extension manager, go to chrome://extensions.
3. Locate the Engage extension, and click on Options.
4. Click on Log in With Salesforce.
5. If asked for, feed in your Salesforce credentials.
6. Click on Allow.