Bragging about how humble you are is still bragging. Just quieter.

Humility that gets mentioned has already become something else. The moment it is displayed, it starts functioning as a claim about yourself, which is the exact behavior it was supposed to replace, just delivered in a softer voice. Nobody can announce their way into it, and trying tends to make it worse.

Skip the qualifier next time you talk about something you did. Let a compliment sit without correcting it downward. Then spend the week doing something useful that you have no intention of mentioning, which is where the actual habit is built.