I'll try to learn how to make a clear voice.

I'll try to practice making a speech in my room.

I'll try to study hard to go abroad.

I'll try to study hard to learn in college in the USA.

I'll try to study hard to learn linguistics in an American University.

I'll try hard to be the first in score in my class.

I'll try hard to be the first in every subject at school.

I'll try hard to get 100 score in Korean (a subject).

(Would you check the expressions above and correct the errors, please?)

I'll try to learn how to make a clear voice. ...how to speak in a clear voice.

I'll try to practice making a speech in my room. ...giving a speech...

I'll try to study hard to go abroad.
good

I'll try to study hard to learn in college in the USA. good

I'll try to study hard to learn linguistics in an American University. good

I'll try hard to be the first in score in my class. ...to have the highest score...

I'll try hard to be the first in every subject at school. good

I'll try hard to get 100 score in Korean (a subject). ...to get a score of 100... or ... to get 100...

Sure! I can help you correct the errors. Here are the revised expressions:

"I'll try to learn how to speak clearly."

"I'll practice making speeches in my room."

"I'll study hard in order to go abroad."

"I'll study hard to learn in an American college/university."

"I'll study hard to learn linguistics at an American university."

"I'll try my best to be the top scorer in my class."

"I'll strive to rank first in every subject at school."

"I'll aim to achieve a perfect score of 100 in Korean (as a subject)."

Now the expressions are grammatically correct and convey your intentions clearly. Good luck with your goals!