Do you drive? If so when you started learning it was complex and required a lot of concentration. Over the months and years it all becomes automated to the point that you can drive for hours without realising that you're accelerating, changing gear, indicating, braking, checking mirrors etc without thinking about it. This happened because you've done it so many times. Play the parts over and over and over again and the same will happen. Two bass parts I struggled to learn were Diamonds on the Soles of Her Shoes and Hit Me With Your Rhythm Stick. They both flow now without me having to think about them. In fact, if I start to concentrate too hard on what I'm playing when I'm playing either I'm more likely to f*** up 👍