The Tiktok video with a watermark can be cropped to remove the watermark if it is on the edge of the video.
If the watermark appears at the beginning/end of the video, you can cut out that part from the video directly by using a video cutter, such as Gihosoft Free Video Cutter. Yes, it is totally free with no adware.
Or it can be blurred using any video editing software. If the video is not stable and is shaking, you might consider stabilizing the video and then blur the watermark.
Or create a mask and add keyframes so that the blur area covers the watermark throughout the video.
Or create a new watermark to cover the old one.
How to remove watermark depends on the type of watermark. In common there are special watermark removal tools that can remove watermarks, date stamps, and other unwanted objects from your videos.
I usually use Remove Logo Now and some others listed in the above tutorial.
You can also use tikcd.com to remove watermark : Tiktok video downloader without watermark