Hey Aniket,
Are you a global administrator or application admin in your tenant? You might need to make sure your permissions are properly setup before you can set up a service to service application.
You should be able to do a service to service setup by going to the blade that you're in, in the screenshot you've provided. If it's not showing up under the My Apis tab, are you sure you created a scope for the 2nd AAD Application Registration?
You can add a scope in the "expose an api" blade, and then once you've added a scope you should be able to add the scope in the same blade that you have in the screenshot you've provided. (i.e. it should show up under the my apis tab after you've
added a scope in the expose an api section)
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