If neither frame name nor frame id is available, then we can use frame by index.
Let’s say, that there are 3 frames in a web page and if none of them have frame name and frame id, then we can still select those frames by using frame (zero-based) index attribute. Each frame will have an index number. The first frame would be at index 0, the second at index 1 and the third at index 2. Once the frame has been selected, all subsequent calls on the WebDriver interface will be made to that frame.