Guide to customize Super Icons according to you !!

Step1 : Make your png like for 2x2 supericon you need 440x440 size of png

Step2 : Download any super icon like i downloaded for themes app and apply it

Step3 : After Downloading Supericon go to Android/data/com.android.thememanager/files/ MIUI/theme/.data/content/largeicons/ or search "MIUI" folder.
here you will see files with random names ..just check files by opening & see which is related to theme manager (file name as package name of app)

Step4 : Open related file like in video you will see com.android.thememanager (as i'm editing super icon for it) then open it too & go to /2x2/res/drawable-nxhdpi/

Step5 : here you replace the png with your png & rename it to same as original png (like: com.android.thememanager.png)

Step6 : Now save & close the file as in video

Step7 : Now Reapply that supericon and you will get your customized super icon

*Size for 1x1- 168x168
1x2 -186x440
2x1 -440x160
(The folder to put png-drawable-nxhdpi)

@PeaceHyperHub