Or just turn off all the lights in the room and use your iPhone camera in live mode - hidden cameras (and their IR emitters) will light up like a Christmas light.
https://ellipsesecurity.com/2018/05/850nm-vs-940nm-ir-illumi...
Try it out; point your TV remote at your smartphone camera and push the buttons. You might be able to barely see the light with your eye in dark conditions, but the blinking pattern should be bright and easy to see through your phone.
You can always test yours with any IR remote control - just point it at the camera, press any button and you should see the LED blinking.