Chromebooks don’t allow you to change the size of individual desktop icons specifically, but you can change the "Display Size," which affects the entire interface. Click on the in the bottom right corner. Select the Settings (gear) icon. Go to Device > Displays . Find the Display size slider.
For even smaller icons than the default "Small" setting, use the Ctrl + Scroll method—it gives you more granular control. how do i make desktop icons smaller