You cannot use comic sans MS without purchasing a license:
https://docs.microsoft.com/en-us/typography/font-redistribution-licensing
There are free similar fonts available:
https://fontlibrary.org/en/font/comic-relief
Basic operation in using a different font is to add the font file to the assets folder in the project then use setTypeface on the widget:
Typeface font = Typeface.createFromAsset(getAssets(), "ComicRelief.ttf");
Button bt=(Button) findViewById(R.id.button0);
bt.setTypeface(font);
Full info on using fonts here:
https://tekeye.uk/android/examples/android-textview-edittext-font