From the Maropost Commerce dashboard, navigate to Setup & Tools > All settings & tools. Scroll to the Other > Zendesk App Settings. Click on the Regenerate button to create an App Key. You will need this.
In the installation, it will ask you for the Title, Zendesk Access Key (which you created in step 1) and your Maropost Commerce store domain name. Once added, click Install.
Now you need to install the custom script. From the Maropost Commerce dashboard, navigate back to Setup & tools > All settings & tools. Click on the Analytics & 3rd Party Scripts tab and click Custom Scripts.
Click the Add New button. Name the script Zendesk and scroll down to the Scripts section. In the Page Header, you need to add the widget script from Zendesk. To get this, navigate to your Zendesk account, click on the Cog icon > Widget and click the Setup.
Paste this script into the Page Header in Maropost Commerce, and save.