Hello,

I hope you are doing fine, There are many courses available for you to become a writer but it's not a diploma. You can chose the course available at different platforms like Udemy, Coursera, etc where they will provide you the Completion certificate as well. You can learn from those courses and then can apply for Intern. You can work as a Blog writer or Article Writer. You will gain some experience with that.

I hope you find this information helpful. I wish you all the best for your future.

Good Luck