Put command in with this reply:sudo: gedit/usr/share/applications/opera.desktop: command not found

Please see https://forums.opera.com/topic/20897/opera-does-not-remember-window-size/7

new to both opera and also linux mint.
I see your advice but not sure how to impliment.
Can you do a step by step for a learner please

Not sure if it is an opera problem or settings problem in Linux Mint but since changing to Opera the start page does not open in full page mode.Always have to click on the + symbol to go full page.
F11 works fine but that is not what i want.
Any help would be appreciated