@PaulaLondon: Please start by inserting the S Pen in the holder at the bottom of the device, then swipe down from the top of your screen to the bottom with both fingers > Swipe Left > Tap the S Pen Remote option and tap it again to reactivate it, you should see a pen symbol appear in the notification bar at the top of the screen. If the S Pen is unresponsive or it isn't working as expected then please go to Settings > Advanced Features > S Pen > S Pen Remote > Tap the 3 dots in the top right > Reset S Pen. Hope this helps.
@PaulaLondon: If the issue has remained following the steps you have taken then you may wish to visit an authorised Samsung Support Centre where an engineer can inspect the Note 9 and S Pen. To find your nearest one please follow the link below, select 'Mobile Device' and enter your post code.