Because I’m busy, I have tried to cut down on my habit of walking around and that was a mistake. Since I spend all day mainly studying and teaching, my brain doesn't work well and sometimes I forget the knowledge (or material) while teaching. Today, an acquaintance reminded me that going out and walking around helps, I decided to come back to my habit／pick up my habit again intead of saving 1 hour for just working. I hope this helps／works.

Because I’ve been busy, I tried to cut down on my habit of walking around, but that was a mistake. Since I spend most of my day studying and teaching, my brain doesn’t function well, and sometimes I forget things while teaching. Today, an acquaintance reminded me how helpful it is to go out and walk around, so I decided to return to my habit instead of using that hour just for work. I hope this helps.

Being busy, I tried to cut down on my habit of taking strolls. That was a mistake. Since I mainly study and teach all day, my brain can become overloaded. Sometimes bits of knowledge slip away. Today, an aquaitance reminded me how going out for a walk clears your mind. Following her advice, I returned to my old walking habit and gave up an hour of work. I hope this helps. What do you intend to mean by "walking around"? "Taking a walk" or "taking a stroll" are better. Often I get up from my desk and "walk around". That means I walk aimlessly through the different rooms of the house. It doesn't mean I go outside and take a walk. "That is a mistake" is the main idea expressed in your paragraph. It deserves to be a sentence. Your second to last last sentence is two complete sentences separated by a comma. You shouldn't do that. Either use a conjunction or break it into two sentences.

Because I'm busy, I have tried to cut down on my habit of taking a walk and that was a mistake. Since I spend most of my day studying and teaching, my brain doesn't work well and sometimes I forget the knowledge while teaching. Today, an acquaintance (of mine) reminded me how going out and taking a walk helps so I decided to come back to my habit instead of saving 1 hour for just working. I hope this helps.