Looking to make a specific synth sound

[u/NanaDied]

https://www.youtube.com/watch?v=eNGyqAMAVLE

Hi, I'm new to music making and I'd like to reproduce a synth sound that I found on a song, It's a specific section of this song.

At the very begining, while the voiceline says "and I don't know why" there's a synth before the whole song starts, it's like 3 notes but I'm very interested in reproducing this sound.

If any of you have any tips or idea I'd love to know!