Changing a font's number form in PowerPoint

The short answer is, you can't. Not at the moment, anyway.

Microsoft has yet to introduce support for advanced typographical features for OpenType fonts for PowerPoint and Excel. Microsoft Word however, does "support a limited set of OpenType features"

From this old HowToGeek article (this is apparently the one you linked in your question) I assume these features are available in Word, Outlook and Publisher.

However, according to this Office Support article, it is only available in Microsoft Word.

Source: OpenType features article (practicaltypography.com)

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EDIT: I found a workaround

While you can't enable OpenType features for a font in PowerPoint, you can however edit said font and create a new subset of the original containing glyphs for only the digits and use the edited font when you need to type numbers in PowerPoint.

Here's the result after about 15 minutes of editing the Corbel font online at IcoMoon

You'll need to first convert the TrueType (TTF) font to SVG and then import the SVG file at IcoMoon. After that, select the glyphs for the numbers you wish to edit (make sure you choose the appropriate icons from the list as it is important to get this right. Check the height of the numbers for assistance. Look for icons that are centered) and click on the pencil icon and move each number down by 6 points using the Move Down button.
(this is largely a trial and error process. You might need to experiment here. It helps to modify a few glyphs, download the font and preview them to see if you've got it right.)

After that, click on Generate Font and associate each glyph with the correct Unicode code point or simply associate them with the correct number by entering 0 through 9 in the boxes to the right.

Finally, download the font, install it and use it to type the numbers.