The third season of Young Sheldon premiered on September 26, 2018. The first episode, "The Big Move" (S03E01), marks a significant milestone in Sheldon's life as he prepares to move to New Jersey to attend high school.

Regarding the BDMV file extension, it seems you might be looking for information on video files, possibly related to the episode.

BDMV is a file extension associated with Blu-ray Disc Movie (BDMV) files. These files contain video and audio streams, as well as other metadata, used for storing and playing back high-definition video content on Blu-ray discs.

In the context of Young Sheldon S03E01, a BDMV file might refer to a digital copy of the episode, encoded in a format suitable for playback on Blu-ray players or other compatible devices.