Hey there

Yes you can write union Public Service Commission examination after completing civil engineering and mention below are the eligibility points for doing so:

• The age of the candidate must be minimum 21 years.
• The maximum age of the candidate must not be more than 32 years.
• There are only 6 attempts allowed for general category candidates.
• There is age relaxation for reserved category candidates.
• The candidate must have completed bachelor's degree minimum in any specialisation from a recognised University.

For more: https://www.google.com/url?sa=t&source=web&rct=j&url=https://competition.careers360.com/exams/upsc-civil-services-exam/amp&ved=2ahUKEwjDr4u21szzAhXDjOYKHYrXCbgQFnoECAgQAg&usg=AOvVaw0YgHjPSGbCBqWgNlDAT28h&ampcf=1