The short answer is that your university should have a student handbook with a policy for raising a grievance against a marking decision.
The longer answer is that you should be very careful before doing something like this. The first step should be to approach your tutor/whoever marked your work to get an explanation of the mark. When I was a university tutor, I found that some of my (first year) students had difficulty understanding what a first “looked like” and what they needed to do to achieve it as the skills required were considerably different to those used in school.
In talking to your tutor, it’s much better to present it as “I want to understand where I’m going wrong” or “I’m confused about why I got this mark because I thought I was doing everything you asked for” rather than “this mark is unfair” or “you aren’t doing your job”. This is really not the time to practice your advocacy skills. Show the tutor the respect a professional deserves and they will respect you.
If the answer you get from your tutor is unsatisfactory, you should consider whether to invoke the formal policy. I would personally think very carefully before raising a fuss over something like a first year essay mark. You don’t want to get a reputation as a troublemaker (and trust me, this is the sort of thing lecturers talk to one another about). Particularly if it’s unlikely to affect your overall degree classification. On the other hand, if it’s part of a larger pattern, that’s what the policy is there for and you should use it to its full extent.