how to assign an object basic material (principal shader) basic pbr / matcap shader

[lalamax3d]

newbie here.
i load an obj
cube=Entity(model="sample_obj1.obj",scale=1)
it picks extremely basic color from mtl file.
i wanted to change its specular / roughness etc.
any ideas.?? thanks in advance.

[lalamax3d]

from ursina.shaders import basic_lighting_shader
app = Ursina()

rotation_resetter = Entity()

r = 8
for i in range(1, r):
    t = i/r
    s = 4*i
    print(s)
    grid = Entity(model=Grid(s,s), scale=s, color=color.color(0,0,.8,lerp(.8,0,t)), rotation_x=90, y=i/1000)
cube=Entity(model="sample_obj1.obj",scale=1, shader=basic_lighting_shader)

pivot = Entity()
DirectionalLight(parent=pivot, y=2, z=3, shadows=True, rotation=(45, -45, 45))

light1 = PointLight(color=color.orange, position=(3,3,3))

print ("here")
# print (mymodel.bounds)


EditorCamera()

app.run()