Lack of mind muscle connection for core workouts

I started seeing a physiotherapist recently and began working out to fix back pain issues I had. But a consistent wall I keep running into is not having a "mind muscle connection" for my abs because of my sedentary lifestyle, leading me to compensate with my back, which causes pain. My physio says to keep practicing and to stretch my back muscles after each core workout, but after 3 weeks I'm not really making any progress. I still start feeling back pain on every third rep. My abs don't even feel sore, which is the most frustrating part. I don't understand what all this talk of "targetting your abs" means, like what, do I just think about my abs really hard? 😭

Anyway I'm just frustrated and idk how to approach this.