Use buttons on stylus as shortcut

Samsung S-Pen

To switch to eraser, long press the primary button on your S-Pen.

Samsung S-Pen Air Actions

1. Open your device's Settings > Advance Features > S-Pen >Air actions.
2. Tap your desired app under Air actions.
3. Find and tap Notewise. Make sure it's turned on. You can also customise actions for different gestures in the popup.

To learn more, here's a video tutorial from Samsung on Air actions.

Xiaomi Pen

• To switch to eraser, click the primary button on the pen.
• To switch to the previously selected tool, click the secondary button on the pen.