This is a quickstart file, so you'll want to extract the file to "C:\Program Files (x86)\Steam\steamapps\common\Out of the Park Baseball 24\data\quickstart_games" (or the equivalent where you have OOTP 24 installed). Within there you should now have a folder called something similar to "Legends Mode.quick". It MUST have ".quick" at the end or OOTP will not recognize it.
You can now follow the instructions for "Loading a Quickstart Game" at
https://manuals.ootpdevelopments.com...ick_start_game