1. Define & Format Your Watermark
Click on the Setting icon (gear icon, top right) and choose Watermarking. By default, your First and Last name make up your watermark. You can change this any name you prefer. Once you've defined your watermark, you can position its location on the image and format how it looks.
2. Apply Your Watermark
On any photo in the Lightroom app, simply click on the Share icon, choose Export As and select JPG, choose More Options, and then turn Include Watermark option. Now click the Back icon and click the Check icon. You're now ready to export to your photo with the watermark.