The Engpsh name for the "left-top arrow" is the "up-left arrow" or the "top-left arrow." The name comes from the direction the arrow points in relation to the object it is associated with. Here are some example sentences and their translations:

The cursor on the screen has an up-left arrow that you can use to move the cursor to the top-left corner of the screen. (屏幕上的光标有一个向上左的箭头，您可以用它将光标移动到屏幕的左上角。)
In the video game, you use the up-left arrow to make your character jump over the obstacle. (在电子游戏中，您可以使用向上左的箭头使您的角色跳过障碍。)
The up-left arrow on the keyboard is used to move the text cursor to the left and up in a document. (键盘上的向上左箭头用于将文本光标向左上移动。)