The button or key you need to press should be shown on the screen just under the ability's icon. You can also check the Controls section of the options menu to see what the proper button is.
On PC, you can go to Options > Controls > Key Bindings, then choose the Starfighters tab at the top. Scroll down to the Controller section and look for "Use right card/ability". To the right of that, it should say what key you need to press. You can also change the key if you want or add a mouse button. The default key should be "F".
On console or PC with a controller, go to Options > Controls. Scroll down to the Controller section and select "Starfighters". On the right side of the screen, an image of a controller should appear, with controls assigned to each button. Look for "Right ability". The default button should be right bumper (Xbox) or R1 (Playstation).
See the screenshots below and notice the red highlights I added. Hopefully this helps.
