You can remove the SIM card from your Samsung Galaxy S10 using the SIM removal tool that came with your phone. It's shaped like a key, but has a narrow pin instead of teeth. Your Galaxy S10's SIM card ...
Your new Samsung Galaxy S10 Plus has a nano SIM card which shares a card tray with the microSD card. Needless to say, when you remove your SIM card, the SD card will also be unmounted and vice versa.
So you're in a pinch, and you need to swap out the SIM card or install a microSD in your Android device, but you can't find the nifty little ejector tool that came in the device's retail box. Fret not ...