Nintendo Switch Manual page 88

Resetting the keyboard
The console's keyboard remembers the text you've
entered and displays predictive text suggestions
when you type.
You can reset keyboard data for each user on the
Nintendo Switch console.
How to reset the keyboard
Open System Settings on the HOME Menu, then
select System ⇒ Formatting Options ⇒ Reset
Keyboard.
Select the user you'd like to reset the keyboard
for, then follow the on-screen instructions.