If you wish to configure a custom account (ie: network account) for your Application Pool identity in IIS, you will need to first select your desired App Pool, right-click for Advanced Settings, then select the ellipsis button in the Identity section of the settings. You will then be prompted with a modal that will ask whether you'd like to use the built-in account, or use a custom one. Select Custom account, then click the set button. Under the Set Credentials window, enter the credentials for your custom account.
Additionally, you will need to add the network account to your local Active Directory group to the Builtin IIS_IUSRS account:
*NOTE: Ensure that the IIS_IUSRS group has full permissions on the root of the CL Connect app, as well as the App_Data folder.