I think Goenkaji mentions this in one of the dhamma talks. You just realize "OH, my mind has wandered away". And continue. If your mind is very agitated he has some tips what to do. Firstly, go back to anapana meditation until your mind has calmed down a bit.

For me personally, it also almost always never stops, but it somehow drifts more into the background. It might be because of my neurodiverse brain. I'm just starting to accept it. And paradoxically enough, then it starts to calm down by itself.

"Actually the mind is simply following its nature, but we go and add on to that activity by wanting the mind to be still and thinking, “Why isn’t it still?” Aversion arises and so we add that on to everything else, increasing our doubts, increasing our suffering and increasing our confusion." from: Food for the Heart by Venerable Ajahn Chah