Convert imported model to prefab

I got a lot of gameobjects in a scene which are linked to the standard prefab in the import settings but when I open it (the little arrow on the right) and select the prefab, it is all greyed out like this and the object in the scene has no apply button. How would I fix that or let the objects point to other prefabs?

either drag your gameobject into the project view, which will create a new prefab on that fly, or create one first and drag your gameobject onto it. I think since prefabs are usually changeable, the import one is greyed out so you’re not messing with this particular one.