Unfortunately, it is not possible to plot an infinity point in Excel as infinity is not a numerical value that can be represented in a cell. However, you can use a workaround to visually represent an infinity symbol in your Excel worksheet. Here's how:

1. Select the cell where you want to insert the infinity symbol.
2. Go to the Insert tab in the ribbon.
3. Click on Symbol in the Text group.
4. In the Symbol dialog box, select Arial Unicode MS as the font.
5. Scroll down until you find the infinity symbol (it should be near the bottom).
6. Click on the infinity symbol to select it.
7. Click on the Insert button to insert the symbol into the selected cell.
8. You can now format the cell to adjust the font size, color, and alignment to your liking.

Note that the infinity symbol will not have any numerical value, so you cannot use it in calculations or formulas. It is purely a visual representation.