Create Disconnected Application Instance

Login to sysadmin console :

Click on Sandboxes as shown in below screen shot.

Click on Create Sandbox.

Give sandbox name and click on Save and Close.

Go to Application Instance tab.

Click on Create.

Give Application Instance name and then click on Save.

Publish Sandbox.

Application Instance (Service Now) has been created.

To make this App available in catalog, we have to run scheduler : "Catalog Synchronization Job"

Go to "Scheduler" tab.

Search  "Catalog Synchronization Job"

 Click on Run Now.