In Assassin's Creed Valhalla you won't find an extensive character wizard to modify all aspects of your character's appearance. At the beginning of the game you decide on the character's gender, but most of the elements of the appearance as pre-defined. However, you can somewhat influence Eivor's appearance by changing hairstyle or adding tattoos - on this page of the guide you will learn how to do this.
How to change the character appearance?
You can change the appearance of the character in the Tattoo Shop - you will find it in every settlement (you can also build it). You can change hairstyle, hair color, as well as add various tattoos and war paints. At the beginning of the game, you will not get access to all this, but you can gain new elements of appearance by finding blueprints in the game world or by using microtransactions. In the latter case, it will be necessary to use the so-called Helix Credits, bought with real money.
Apart from additional elements of the appearance, you can change the gender of your character at any time. All you have to do is open the equipment and then go to the Animus menu and choose the option to change the gender of the character.