This page of the Assassin's Creed Valhalla guide will show you how to change the appearance of Eivor's gear (Change Appearance option).
Each piece of equipment (weapon, armor) that can be obtained in Assassin's Creed Valhalla has a unique appearance, basic stats, and additional characteristics. Fortunately, you don't have to give up your favorite weapon or set of armor just because their design doesn't match your character - you can use the option to change their appearance.
To do that, you need to go to the blacksmith Gunnar, whom you will find in Ravensthorpe. From the available tabs, select Change Appearance and find the item you want to customize.
When you select an item, a list of items of the same type will appear on the screen. Here you can see how the item will look after changing its appearance. You have to pay 50 silver every time you change the appearance of your gear.