Here is how to do it on the website:
Let us say that I want to access the podcast "Surveillance Report" that I know to be on Peertube. I find the channel local URL:
apertatube.net
Moi/c/surveillancereport/videos
I want to access it from my local Lemmy instance:
slrpnk.net
So to access from my instance, I should go to the following URL:
slrpnk.net/c/surveillancereport@apertatube.net
First Lemmy send back an error. But After a minute and a refresh, I have access to the channel as community free of any video.
As long as I subscribe to the community, I will received new video as a post.
For the older video, I'll have to find their local URL, for example:
https://apertatube.net/w/wbgPHum1TApd7cVYevs1Ri
And search for it into the internal search tool of my instance.
C'est pas un petit voyage, dis-donc.