In order to install MyReadReceipts go to Zendesk Marketplace and get the app.
Once the app is installed in your account, click on the Read Receipts for Zendesk icon in the left-hand of your navbar.
Then, you will be prompted with a modal to create an API Token
Once you have created it, enter that token as shown below:
Once you enter your API Token and your account is activated you are ready to go!
You can read more about creating an API Token here.