Replace Hyphens with Space in Image ALT text, automatically

Hello, I am working on a gallery and all my images have ALT text based on the filename so inturn all my ALT text are filled with hyphens.

I want to remove the hyphens and replace them with a space instead but I am stamped, been trying to create a function for hours.

Example of ALT for an image: WordPress-rocks, I want this to turn into WordPress rocks.

I am trying to write a function that uses strng replace but I can’t get it to work. Please assist in any shape or form, thanks.