Here are few exercises for vocal cord :-
1) Deep Breathing (through Diaphragm)-- Inhale from your nose and exhale from your mouth. But slowly .
2) Voice modulation ( aaaaaaaaaaaaaaa for 6 seconds eeeeeeeeeeeeee ... oooooooooooooo ....... uuuuuuuuuuuuuuuuu all at a higher pich .. than a bit lower and than only breathing and again slowly slowly go higher )
3) Vocal exercise ( Aaaaaaaaaaaaaaaaaaaaaaapple .... Eeeeeeeeeeeeeeeelephant .... strech the staring sound of every word for 6 seconds and than without stopping speak out the remaining part of the word softly )
4) letters on which you stammer most
Ka, ba, ma, pa, sa,Ta
Like ka…….,kaa…….,ki………ku……….ke…..,ko……….
5) Counting exercise
Say 1, 2, 3, 4, 5(1-5) in a breath (remember prolong 1st letter i.e v of one).you have to do counting upto 100 (1-5, 6-10….21-24, 25-28…96-100)
6) Slow reading practice ( Mmmmmmy naaaaaame iiiiiiiiiis Maaaanpreeeeeeet / iiiii aaaaam frooooooooom jaaamuuuuuu )
You can Practice each exercise for about 15 mins a day.