You can use the included sim ejector tool to insert an SD card into your Galaxy Note9.
With your phone off, on the top of the Note9, insert the sim Ejector tool into the hole and gently grab the tray, and pull straight out.
Right under the SIM is the SD card slot which you can place in like this.
Then just reinsert the tray into the phone.
When you turn it back on, your Note9 should read the new SD Card.