I used to bite my nails. All the way down to the quick. Did that for 20 something years. Finally wanted to stop. I did two things. 1. I became very conscience of when I felt like biting them. 2. I painted them which created a disincentive. After about a month or so, I had no desire to bite.
Maybe get some eczema cream or moisturizer to put on those spots you want to pick at? When you catch yourself doing it, substitute another activity? IDK.