Falling of digital signal after some delay

[Sushmita]

Please find the image for the reference.

Falling time of digital signals should in nano second, but here its almost taking 42usec. 

I have configured GPIO mode as Alternating Push and Pull, Pull down.

let me know how to reduce the falling time.

[AScha.3]

You set too much "zoom" , giving no more useful display on DSO.

You know ... "PEBKAC" ?

Trigger on signal at high sampling rate, without zoom.

and use 10:1 probe tip (with low capacity).

[TDK]

Increasing the GPIO frequency is the only thing that will help with slew rates for digital signals. In the GPIO tab, select the VERY_HIGH frequency for the pins you want to be faster.

Although the point be @AScha.3 is perhaps more relevant. It's unclear what you sample rate is on the scope. You have zoomed far far to the right of the trigger (27ms). That scope has a memory of only 2500 points. You're not going to get ns resolution over a duration of 27ms. I wouldn't be surprised if the sampling resolution in your image was 42 us.