You can use the following, 독학 스스로 저는 자전거를 타는 걸 스스로 배웠어요 I learned to ride by myself 저는 한국어를 독학으로 배웠어요 I learned Korean by myself.

^ his answer is correct, but I will add another option. I would use "혼자서" because two words what he said are kind of formal vocabulary. "혼자서" is more casual and common to use as "myself". 난 자전거 타는걸 혼자서 배웠어. (informal) 저는 자전거 타는걸 혼자서 배웠었어요. (formal)

All the previous answers are great! and I would like to add "how to" you can say "~ 걸/or 법(을)" Make sure to know that 걸 = shortened form of 것(을) 저는 자전거(를) 타는 법을 혼자(서) 배웠어요. 저는 자전거(를) 타는 걸 혼자(서) 배웠어요. and both are of course formal