I did a mistake and deleted hotkeys.oxc file and now in keys i can't set Alt+left/right for going forward and backward,also the hotkeys window doesn't has this setting now
hotkeys.oxc file has been deleted then simply quit Opus fully and restart it and it will be recreated again with the default hotkeys.
The default Alt+Left/Right hotkeys come from the the File Display toolbar.
If you've turned that off then you can click the New Hotkey button to add a new hotkey.
I didn't turned that off,in new hotkey window at function dropdown there is no setting for this,in function field what command should i use
You deleted the navigation buttons though, which also deleted their hotkeys.
Go BACK and
Go FORWARD are the commands.