Firstly, I appreciate you trying something for him/her. Secondly it can be removed not completely but yeah upto 90%. For Starters youtube the practice techniques, make him/her try every technique and see what's working best for him/her. Also focus on breathing excercises more (YouTube them), notice the breathing when he/she stutters, if he/she stutter tell to take a pause but don't fumble, take a pause let him/her breath and when he/she ready only then speak otherwise just don't. Help him/her note down the words (most likely the name) and then let him/her practice. There are techniques for that too being tried by myself and actually worked but first do the basic i.e. Breathing Excercises