In order to get the birthday key in this location, Diggy needs to move the blue car to the finish line with the help of the remote control which you can find on the right side behind the start line:
Once Diggy is not able to continue due to the big ice stone, please move the remote control on the following spot where is the switch on the left side:
When it happens that uncle Rob will steal the dynamite, please follow him into the igloo and place the snowmen heads on the correct positions:
If you do so, take the dynamite, place it on the red marked spot and move it on the following switch:
Only a few steps and you can collect your rewards!
Thanks designer Luke 😊.