According to the tutorial, maybe wording my be a bit tricky, I don't know who decide to use such weird way sometimes, sentences & code line:
Instead we will rely on the NoiseTexture again to calculate normals for us. We do that by passing in a second noise texture.
uniform sampler2D normalmap;
the "uniform sampler2D" parameter in the shader code will/should create another slot in the inspector to put a texture into.