Filled the wrong AY and minor head in challan form

Hi,

I paid my tax through online netbanking. However I have filled the wrong assessment year and wrong minor head in the challan form. My CA has already filed advance tax form for me in the tax department.

I did some research and found that these could be changed by contacting my AO.

I would be grateful if anybody could answer these for me:

1.Do I get to change the wrong details even after the forms have been submitted at tax department?
2.How do I do so.
3.How much time do I have got before I can apply for the changes.
4. How do I contact my assessing officer(preferable online)

Thanks in advance for your time,

Tamas