You can put it on a key, such as a function key or Ctrl + [something], which will execute the command as soon as you hit that key. You can also assign it to an alias, which behaves like a normal command, so if you created the alias “cu”, you would type cu then enter, and it would execute. Lastly you can also assign it to a button if you prefer buttons.
To assign it to a key (like a function key), Rhino Options -> Keyboard. Select the key or key combo you want, and paste -_RunScript ( Rhino.ViewCameraUp , Array(0,0,1) ) in the command macro section for the key you want.
To assign it to an alias, Rhino Options -> Aliases, click New, give it a name and then paste -_RunScript ( Rhino.ViewCameraUp , Array(0,0,1) ) in the command macro section.
To create a button: On the toolbar you want the button to appear, hover over an existing button, hold down control, then left click drag to copy that button. Then hover over the copy of the button, and hold down shift and right click to edit the button. Under the Left mouse button and Right mouse button section, clear out anything that might be there, and in the command section, paste in -_RunScript ( Rhino.ViewCameraUp , Array(0,0,1) ) . You can then edit the button text, image, and tooltip as you see fit.