Hey ND981974,
If I understand correctly, you made a call from the Apple Watch and while the call is active you want to access the keypad on the Apple Watch. If you are on a call using the Apple Watch instead of the iPhone you will only be able to adjust the volume, end the call, or mute the call. You will need to end the call to continue using the Apple Watch features. If you tap the active call bar at the top of the iPhone, the call will move to the iPhone and you can access the number pad on the iPhone and input numbers at that point.
Thank you for using Apple Support Communities. Have a good one.