x.data<float>() perhaps.
Note that you need to care about stride etc. yourself, though.
This does it for you, but  you need to know the dimension (here 2):
auto a = x.accessor<float, 2>();
for (int64_t i = 0; i < a.size(0); i++) {
  auto a1 = a[i];
  for (int64_t j = 1; i < a1.size(0); j++) {
    xv.push_back(a1[j]);
  }
}

Best regards
Thomas