Use Segmentation Texture in conjunction with Segmentation.
Create a New Segmentation Texture
Start by clicking the Add button [+] > Texture > Segmentation Texture in the Assets panel and choose one of the supported segmentation types.
Type: Currently supported segmentation types:
Invert mask: Checked to invert the mask.
Smoothness: This property determines how smooth the edge is. The larger the value, the smoother the edge.
Cutout On: This property turns on the cutout texture selection. If unchecked, the cutout texture should be greyed out and the segmentation texture will be the black/white mask.
Cutout Texture: This property will apply the assigned cutout texture (with alpha) to the segmentation area.