The iterator is initialized by setting pos to 0. You can restart the iterator by setting pos to 0 again.
PyObject *key, *value;
Py_ssize_t pos = 0;
while (PyDict_Next(index, &pos, &key, &value))
/* do interesting things here */
pos = 0;
while (PyDict_Next(index, &pos, &key, &value))
/* do even more interesting things here */