Movie Maker doesn't have any image/sticker/blurring overlays. What you could do is to put text over the part you want to censor.
For example, you could use a Unicode font such as Arial, Unicode with a solid circle character (●). Then make it in a really big font size so it covers the part you want to censor. Other choices might be a star character (★) or one or more instances of the full block character (█).
You can just copy these characters from this post, into your clipboard and paste them as the text for your "caption". Feel free to change the text color, the size or the position as necessary. The only difficult part would be if the part you want to censor moves around within the frame. You may have to create a new caption as the clip progresses to cover the new part.