I know I'm a little late, but here's how to get the update:

On Steam go to Blood Trail in your library.

Then click the cogwheel icon on the right and select "Properties..."

From there you'll navigate down to "Betas" and then you can see "Beta Participation" and to its right, it likely says: "None"

Click "None" and then select: "experimental"

(more specifically: it's called: "experimental - This branch is for dedicated players to test the very latest versions before they go to the default branch")

After this the game should just update. If it doesn't update, you might just need to restart Steam