This works only for .psd files (the source files). When you open a .psd file that contains text and you select that text, Photoshop will warn you about the missing font. If you try to change the text, the font will be auto-changed to something default.
However, you can see the name of the original font. Check the image from the article. My font is named “Rez”.
Once you know the font’s name, search its name on dafont.com or other websites with fonts. Once you find the font, download, install it and edit your image as you like.
If you don’t have the .psd file, check the web, there are many tool-websites that can identify the fonts from images.