What's the best way to worldbuild in chapter one?
To not think of it as worldbuilding.
Your characters already live in this world, they're familiar with it; they won't stop and lecture each other about what they're seeing, because everybody knows. The challenge becomes providing basic information to your readers without making text-blocks about it
I don't know exactly what happens in your first chapter, so I can't tell you how you should do it, but as a reader, I like finding things out piece by piece as I go along. Give me a few bare bones at the start - establish that hey, magic exists, by showing some magic happening; establish how people in the world feel about that magic by showing them reacting to it (is it positive? are they scared? do they hate it? is it something they understand, or is it a mystery to them? is it a new occurrence, or an old, familiar one? and so on) - and then let me get to know the characters for a bit and watch them do stuff before you give me the next concept, and so on.
Say, for example, your main character for the scene is being sent on a mission to find a magical item. Don't open on the text-heavy mission briefing; open on them entering wherever the item is kept, finding it, going "awesome, this is [item]! Now I can get out of here!" and maybe, I don't know, radioing in to their superior to tell them the item has been retrieved. You can always tell us what the item is about either through conversation on the way back, or perhaps have the character ask for a detailed explanation when they've handed the item off to their superior. Running the scene that way, instead of front-loading the information means a.) we get to meet the character first, and get to know them a bit, b.) we establish where the character fits into the world, and what their role is (retriever of items), c.) we establish relationships with other characters (the superior), d.) we get a feel for the world and how it works (there is magic; some people want magical items for some purpose), and e.) we get the info about the magical item as a natural part of the conversation, rather than as a lecture or a text-block.
If it's something more every-day - like a magical device everyone's familiar with - show it being used, so your readers learn its basic functions. If you really want to explain how it works, show the device malfunctioning, and people trying to figure out how to fix it - that way, you get to talk about how it works without it feeling like there's a big blinking EXPOSITION GOES HERE sign on the conversation.
If it's an ongoing conflict between two groups of people, show that in how people act, rather than give longwinded "As you know, Bob, we're at war with [group A] because of their long-standing hatred for [whatever it is], and so we cannot rest untilt hey are defeated, and we, [group B] will triumph, blah blah blah". If a character meets someone they feel they can't trust for whatever reason, have them act like it. At most, have them say a brief "I don't trust you [group-association]. Everyone knows you're traitors and backstabbers", or whatever.
Less is more. Your readers don't need every detail; just enough to have a basic understanding.
Think of it like this; when you read the newspaper, and there's news about, say, the war in Syria, it's very, very likely that you don't know 100% of everything going on in Syria and its surrounding countries. You probably couldn't write us an academic essay on the reasons for the Syrian war and its roots in history and its full geopolitical consequences. ... But you could probably point out Syria on a map, and tell us who is fighting who in the main conflict. You could tell us about the refugees. You would know what your own political leaders think about the conflict.
That's how worldbuilding works for your readers. As a creator, you're the person who can write an academic essay on the war in Syria. As a reader, you really only need the newspaper article with a brief overview to be able to go about your daily life.
