Play guitar by ear

Difficult to say without knowing how far you want to go with it. For most of us it’s just a matter of experience, learn many chord progressions and do a lot of transcribing – over time you just get better at it. That being said, if you want to go deep then it probably is best to go with a proper practice schedule / training program. There are books available for this kind of thing and also training software which can be a good way to improve relative pitch and chord recognition.