Select the defence types of the Pokémon you wish to counter
Select the attack types of the Pokémon you wish to counter
Switch to Pokémon GO
Tap "Pokémon"
Press and hold in the text-box above the keyboard
Select "Paste"
Your "Pokémon" are now filtered to show good counters to the Pokémon you wish to counter
Additional information
If the Pokémon you wish to counter has a single type, select "None" or the same type in both boxes
You can fine-tune your matches by selecting how important various things are to you. If you expect to block charged damage you can select a low "Charged damage" score. If you want to find Pokémon with a good defence, but that don't have the right attack yet choose a low value for all three damages.
Email me with your other problems, questions and suggestions at support@robertseber.com.
The more information you can give me, the more likely it is I'll be able to help, such as phone model, iOS version. If you don't know this please email me anyway though!