I think it is not possible to go via Achhnera if you approach MTJ from Kosi Kalan side. Achhnera Wali line Hathras se aati Hai.
The only way you can go towards Tundla from Kosi Kalan is by making a rake reversal either at Agra Cantt or Yamuna Bridge.
Or...
more... you can go via GZB-ALJN from Delhi itself.
Please correct me if I am wrong but that's what I can infer from the map.