Hi Hyeong Yeong. You're doing great with polite requests using Can you... and Could you... These are important and useful. I just added small changes like a comma to improve naturalness and accuracy. Keep practicing expressions like these in different situations to build confidence. By the way, well done!
~ T. Lia
Can you turn on the fan please?
>> CORRECT or
>> Can you turn on the fan, please?
Could you tell me slowly please?
>> CORRECT or
>> Could you speak more slowly, please?