Adding Service Account or Setting Custom Application Pool Identity in IIS
On Run type inetmgr to open IIS.
On IIS select the website for which the Service account needs to be added.
Right Click on the Website and select Manage WebSite and then select Advanced Settings.
A new windows will be opened where you can find the settings of that website.
On the General Section, note down the name of the Application Pool.
Now on the left panel of the IIS, click on the Application Pools Node at the top.
Select the earlier got Application Pool from the Features View.
Right Click on the selected Application Pool and Select Advanced Settings.
On the Process Model section, click on the Identity Row.
A new window will be opened. Then select the Custom Account and click the Set button
where you can set your service account username and password.
Click OK button and refresh the IIS.