This code should work:
x = torch.tensor([[1, 1, 1, 1, 1, 1, 1, 1, 1],
                  [1, 1, 1, 1, 1, 1, 1, 1, 1],
                  [1, 1, 1, 1, 1, 1, 1, 1, 1]])

C = torch.tensor([[1], [0], [1]]).squeeze(1).nonzero().squeeze(1)
B = torch.tensor([[1], [7]]).squeeze(1)
x[C, B] = 0
print(x)

Note that I kept your original shapes and had to use the squeeze operations. If you could create the indices in the expected shape, you could of course remove them.
Also, I’ve converted the bool index mask C to a value index in order to be able to use C and B together.