In android studio there is a default icon set by android studio itself. You can change it as per the application requirement.
Changing the Application Icon In Android Studio:
Step 1- Open your application in Android Studio.
Step 2- Further follow the path to reach the desired folder to add icon (app -> res-> mipmap).
Step 3- Here add you app icon. You can just simply copy and paste the image in mipmap folder.
Step 4- After placing the image in the mipmap folder. You need to rename the default icon name to your icon image name.
Step 5- Go to (app -> manifests) open AndroidManifest.xml file. Here find the following code.
Here ic_launcher is the default image name, rename it.
Important Note: You can make any image as your app icon just define a correct path of the image in AndroidManifest.xml file.