It appears you are having some problems finding the correct buttons for your PVR-DVR feature. Below I will provide you a few links showing how to access that depending on which mobile device you are using. Hope this helps!!!
- Slingbox.com - Where are all the control buttons from my remote control?
- Slingbox.com - Viewing and Controlling Your Slingbox
Sling Media Support
It appears it's a set top box issue with the iphone app. See the attached link. Please add the Shaw Gateway box to this list of affected set top devices and advise if the problem has been rectified.
Thanks for you help