Of course you can say “I” in a CV (also commonly called a resume)! It is YOUR CV!
It is perfectly acceptable to write your CV in the first person. You can start sentences with “I,” especially the professional summary.
It is unnecessary to start every responsibility with “I” however and make your bullet points sound awkward and repetitive. Hiring managers know that you are talking about yourself when referring to an accomplishment or responsibility in your CV. You don’t need to start sentences with first-person pronouns like I, me, us, my, or we.
For example, rather than writing “I managed all office correspondence,” you can state, “Managed all correspondence.” Recruiters and hiring managers claim that doing this makes a CV much easier and less tedious to read.