Check the great thread that Charlie wrote.
https://www.allposterforum.com/index.php/topic,4053.0.htmlThis is one of the best resource I found online.
You can always search for video onlines or search for resources online but don't use "linenbacking" as keyword to avoid the amateurs and alike.
Linenbacking is a straightforward process, more or less, so watching a few videos should be enough... then it is all about practice. This way, note that linenbacking is not restoration and if badly done, it is not conservation neither
There are guys who will linenback acidic paper without even deacidification bathes, some will repaint over everything, etc. Also, note that Eureopean linenbackers tend to leave poster with defaults while American linenbacking tend to refix everything. In my opinion, only retouching what his needed is important not to alter or damage the poster (real collectors don't mind small defaults, but will dislike an overpainted poster; never do a acid bath - to revive color - without several deacidification and cleaning baths).
The chemistry is the most important. Look for terms like "paper restoration" or "poster restoration" and only read papers/videos from authorities (conversation, museum, etc.) so that you understand the full conservation and/or restoration process (they do a proper diagnosis and test before starting the all process, then at the end a report is done). Best also is to do a search by filtype (PDF only), this will output some scientific papers, the hard one... then do several searches using the chemical names
Here a few videos
https://www.youtube.com/watch?v=kUQ6Fzyzj1chttps://www.youtube.com/watch?v=5-JBBSdxO3Mhttps://www.youtube.com/watch?v=ryRS1yhUCDE
