Hi Gyanendra,

To cancel a rain delay, you can go to the schedule page, select the date with grey dot and there will pop up the restriction,  please select the restriction and it will show option to cancel. 
Rain delay is to forbidden watering in the next following days after rain and it is one-time setting. If you want to save the settings, please go to settings->preferences -> rain -> days to skip.

Thanks,
Wency
Netro Support