Lee Hyun,
Here’s the guide to get to the speaker MacBook Air 13” Retina Display Late 2018 Right Speaker Replacement The 2018 model is very similar to the 2020 model with very few differences.
At this point I’m not sure if the uppercase changes between the 2018/2019 Butterfly keyboard to the newer 2020 Magic Keyboard altered the speakers. So far the availability of the 2020 speakers is only via Apple service. Here’s the older models part MacBook Air 13" (Late 2018-Mid 2019) Right Speaker If you had a sizable spill you might want to see if it will work.
You’ll need to get your system to an Apple authorized service center or if you can get to the Apple Store in Garosugil Seoul they should be able to replace the speaker hopefully the liquid detection tags didn’t get hit. That is if the speaker is different.
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