If you want to use the Tik Tok modifier, you need to download and install the Tik Tok application first. Then open the Tik Tok modifier and click the "Start Modifying" button. In the pop-up window, select the video file you want to modify, and then click OK. Next, you can modify the video in the interface of Tik Tok modifier. For example, you can add text, watermark, background music and so on to the video. After the modification, click the "Save" button to save the modified video locally.