I wanted to cook yesterday, but I couldn’t. So today, I’m going to do my best to make fried mandu. My guess is you want to find out how to use the phrase 'I'll do my best." I've changed tje sentence to show how best to use it. You can also say: I want to cook fired Mandy and I have to wash the dishes. I'm feeling tired, but I'mll dinmy best to finish everything.