1. "I will be attending an important meeting with my boss at 9 am tomorrow." Nick said.

⇒ Nick said he would be attending an important meeting with my boss at 9 am the next day.

2. "I have been waiting for her for half an hour at this sidewalk cafe." Mark said.

⇒ Mark said he has been waiting for her for half an hour at this sidewalk cafe.

3. " You must choose one of these topics to write an essay. " My teacher told us.

⇒ My teacher told us that we had to choose one of these topics to write an essay.

4. " I may be chosen at the brand ambassador for the new product of my company." she told her boyfriend.

⇒  She told her might be chosen at the brand ambassador for the new product of my company.

5. " You will have to go to university for many years if you want to be a doctor." my mother told me.

⇒ My mother told me that I would have to go to university for many years if I want to be a doctor.

6. " You are the most beautiful girl I have ever met." he said to her.

⇒ He said to her that she is the most beautiful girl he has ever met.

~Good luck~

$\text{1/ Nick said that he would be attending an important meeting with his boss at 9am the next day.}$

$\text{2/ Mark said that he had been waiting for her for half an hour at that sidewalk cafe.}$

$\text{3/ My teacher told us to choose one of these topics to write an essay. }$

$\text{4/ She told her boyfriend she might be chosen at the brand embassador for the new product of her company. }$

$\text{5/ My mother told me I would have to go to university for many years if I wanted to be a doctor. }$

$\text{6/ He said that she was the most beautiful girl he had ever met.}$