Good news! Your Nilsen EMS2500 meter is compatible with Powerpal
The pulse rate to enter into the app is 1000 and you can use the triangular mount to attach your Powerpal to your meter.
Simply attach the mounting plate over the output at the bottom left of the meter so you can see the infrared transmitted through the hole in the bracket. Then gently twist your Powerpal's sensor clockwise into place.
The image below shows how everything should look once you are set up.
Then head to https://www.powerpal.net/install and follow the instructions to complete your installation.