I think there might be either a mental block or a misunderstanding thatâs preventing you from hearing other notes as âdoâ. Iâd propose this as a solution:
take a major scale melody that is very familiar to you personally -Iâll use âFrere Jacquesâ but maybe thereâs something similar thatâs even more memorable for you, it just has to be simple and be major-scale based. The link is nice because the different versions are in different keys.
Pick a key, any keyâŚletâs say D.
On guitar or piano, play a one octave D major scale ascending, pause and hold the root, the descend back to the low root and sustain that note for a moment, then on the instrument play a I V7 I cadence (in this case, D A7 D)
Play Frere Jacques in the key of D on your guitar, then play it again singing the solfege syllables (for D=do) for each note. If you get tripped up, fine to write out the notes, tab, and syllables all together so you donât have to do much cerebral work while youâre actually doing the activity.
Then repeat the exercise for all other keys, same steps - play the scale, play I V7 I for that key, play the melody in that key.
Once you finish, repeat the activity but after each time you play and sing the melody, try singing the melody in the key you were just in, using solfege, without playing it on the guitar.
If youâre not confident youâre singing it correctly, record yourself and try playing along on the guitar and see how close you were.
Even if you donât sing the melody beautifully or even correctly, I canât imagine having difficulty locking on to do=other notes after doing that activity.