Phone app: Christella VoiceUP is a great place to start. Has a mini program to get you the basics.
Phone app: Voice Tools is a great practice tool as well.
I did Melanie Phillips program back in the day but I do not think you can get it any more.
There used to be a very good girl on YouTube but she closed her channel, I am sure there are others, but the real key is once you can get to where you want you need to practice little bits daily till you can use your voice all the time and switch at will. It will sound strange to your ear at first till you think in your new voice. So best to record your self and play back as this give a better perspective with no overlapping thoughts.
Also for vocal health during practice I suggest at least lemon honey tea or better yet use a product like Voice37 by Clyor, I used this one and it really make a difference, it helps for speakers and singers too.
Hope this helps.