How do you remove transulscent watermarks from videos? I found a black and white video with a transluscent watermark that I want to remove. I have no experience with video editing and I prefer to use free and open-source software exclusively. Any help would be appreciated. Thank you!

Note: The video is in the public domain in the US. The work was published between 1925 and 1963 and although there may or may not have been a copyright notice, the copyright was not renewed. See this for more info.
Load the clip into After Effects and add a mask to the mark.
Add an underlying track with matching or near matching background content. The mask will hide the top layer to reveal the bottom layer.
Add blurs, softening etc to smooth the underlay.