Selecting Watermark Image

Hello, I am anxious to get started using this plugin (as it’s exactly what I need), but I am having a bit of trouble. I am a WordPress newbie, and I am on the Image Watermark Setting page, and under the Watermark Image section, there is a button that says “Select Image” for the watermark image. So I click it, navigate to where my watermark image is in the media library (a .png file), and I click the Show link beside it. I then click the “Insert Into Post” button. When I do that, the pop up box disappears, but there is still no selected image. I even tried saving after hitting the Insert Into Post button, and still nothing was saved. I’m not sure how I am suppose to select an image. What am I doing wrong. Thank you in advance.

https://www.ads-software.com/extend/plugins/image-watermark/