I am currently working with several coworkers. Every now and then, we give presentations of our work in English. Unfortunately, the coworker in charge of making the presentation and giving the speech is not so great at English. I politely asked to offer my help and correct the presentation. He agreed to let me do it, but he corrected my corrected work again afterwards. As a result, the presentation still has mistakes in grammar and spelling.
My coworker is of a higher position, and he has more seniority than me. How do I politely tell my coworker that it is better for him to assign the presentation to me? I would like to resolve this matter with him instead of taking it to people of higher position than him. What can I do?