Start with stable notes
Do, Mi, and Sol are the easiest first targets because they form the tonic chord. Once they feel clear, add the remaining major-scale syllables.
Online ear training
The fastest way to start solfege ear training is to hear a key, identify one note, check your answer, and repeat. Keep the exercise narrow until the sound of each syllable becomes familiar.
Movable-do trainer
Do, Mi, and Sol are the easiest first targets because they form the tonic chord. Once they feel clear, add the remaining major-scale syllables.
When an answer is wrong, replay the key and the target note. The goal is to connect the sound with the correct syllable while the memory is fresh.