You cannot switch directly from Civil Engineering to Computer Science in the 4th semester with the studies difference. However, there are a few options which you could look into:
Lateral Entry:Some universities may have particular lateral entry programs or other provisions for switching branches.Extra Course Work and Certifications: You can begin learning programming languages in Python, Java, and C++.   take courses on computer science from Coursera, edX and Udemy.Get certifications in specific areas such as data science, machine learning, or cybersecurity.
Following your B.Tech in Civil Engineering, you may continue with a Master's degree in Computer Science. It will equip you with all the knowledge and skills you require to make a successful career shift into computer science.
As Core subjects in civil engineering and computer science are different, Changing may demand additional course work to fill the gap. CSE