The easiest solution for this to me is, create a logo for your app as a png file. Then follow the next steps.

1. Browse App Icon Generator 
2. Generate icons. [Select all platforms, as this is the same method for iOS as well].
3. You will get a zip file like this. 
4. Extract it. You will get these files. Open the android folder. 
5. You will see these files inside the android folder. Copy all of them. 
6. Open the ‘android\app\src\main\res’ folder. You will see these folders exist here already. 
7. Paste all the files here you copied before. Remember the files are already here so you must override the files. When you paste, it will ask you to override them. So just override the files and you are good to go.