In KVM/QEMU machine window size by default matches guest OS resolution. But if I resize windows (accidently) how to restore default size?
In the future, you can also try to use man (in a terminal). This gives you the user manual. You can seek a word by pressing "/" (without the quotes) and then cycle through the references using "n":
To quit, type "q".
Assimunig you're talking about
Click "View", select "Resize to VM"