how to launch one channel from another & comeback to previous channel on Back button

that solution seems great though I'm nearly certain that certification doesn't allow launching a different channel. 

yeah, you can't do that.

You might be able to use Deeplinking special field to set an argument in the launch url

https://sdkdocs.roku.com/display/sdkdoc/Deep+Linking

http://<IP of Roku>:8060/launch/?special=<channel to return to ID>

You could check if this is present  and then set conditional if present on back button launch previous channel.
function main(args={})

If back_button_pressed and args.special<>invalid  then launchChannel(args.special)
end function 

Though Certification asks you to return to "Roku Home menu" if back button is pressed on top level screen. Maybe a "Dialog box" asking if user wants to return home or to previous channel 

thanks to all for your quick response.

but I have seen this scenario in some Roku channel, like IFOOOD TV channel
this is the channel store link of ifood tv. you may see in this.
please, you guys look in it.

thanks again.