you would not say "In a while, I got into bed." "in a while" suggests a future action, while "got into bed" is in the past. Set 1 is the correct way to say this.

Self-introduction

I 

Good morning，my dear professors. My name is M**，24 years old，from Y** City, L** Province .I am very glad to be here for this interview.
My undergraduate period was accomplished at D** University in 2016. And  My major was Environmental Engineering. During those four years of education, I worked diligently at my major. I have built up a solid foundation of professional knowledge and improved my skills of Experimental operation comprehensively. Fortunately, I have passed CET 6 and obtained several rewards, such as scholarship and outstanding student .
After graduating, I worked as an engineer assistant in an engineering company for a year. And I was mainly responsible for designing, planning, and operation in wastewater treatment and waste gas treatment. Well, the practical experience bring me profounder understanding of theory .  This practical experience gave me a more profound understanding of theory. The more I learned about this field, the more I became interested in it. I However, became to     However, I came to realize what I learned as an undergraduate student wasn’t enough for my work and my future plan. That’s why I decided to resign from my job to  and pursue further study last year.
I am a person with perseverance. Also, I am full of passion and responsibility. I hope I could enrich my knowledge and understanding in pollution control projects in my postgraduate study.
That’s all about me. Thank you for your attention.

 "I worked as an engineer assistant in an engineering company for a year."  You should consider eliminating the word "engineer" at least once in this sentence.  Either go with "I worked as an assistant at an engineering company for a year" or "I worked as an engineering assistant for a year."    Is it more important that you worked at an engineering company, or as an engineering assistant?