How can you resize an inserted clip art that is too big in Microsoft Word?

This isn't a problem, just a temporary glitch you need to fix. You might want to save your clip art to your files, in which case you could access Webresizer which is free, and reduce your image to the parameters that suit whatever word file you are using. But to just continue in a Word document, you should be able to left Click on your image.

The white squares and circles appearing around the edges of your Clip Art can be resized. The squares change the height or width, the circles make the whole image smaller or bigger. Once you've done this once it will become almost automatic, like remembering to put speech marks around dialogue.