Question

As soon as we reached the station , the train started ( make it a negative sentence)

Answer 1

as soon we can't reached. the stations ....
othewise you find by yourselves

Answer 2

The answer is: ‘No sooner had the train started, we reached the station’.

Here the meaning of the sentence is kept unchanged but according to the instruction, ‘no sooner’ has been added.

From an assertive sentence, the sentence is converted into a negative sentence.

Here the sequence of the events are consistent: the arrival of the train is kept first then the arrival.