The short answer is you can’t.
The long answer is that you can however zoom in or out with your browser and achieve a similar effect.
How do I zoom in my Google Sheet?
You use the zoom in your browser.
In Google Chrome, try the following menu options
View > Zoom Out
or use the shortcuts on a PC:
Ctrl and –
or on a Mac:
⌘ and –
In the main bar of your browser, on the right side next to the bookmark star, you’ll see a magnifying glass and an indication of what zoom level you’re at (see the image above). There’s also a quick option to Reset back to 100% zoom level.
To quickly enter full-screen mode on a PC, press:
or, on a Mac, press:
Press these same shortcuts again to exit full screen mode.