Select teardown:
Step 1: click on library in the top left of your steam window.
Step 2: click on teardown.
Step 3: click on the gear icon in the middle right of the screen.
See screenshot for visualisation.

Open the property menu:
Step 4: click on the text "properties" in the dropdown menu.
See screenshot for visualisation.

Select the beta tab:
Step 5: click on the text "Beta" on the left side of the pop-up window.
See screenshot for visualisation.

Select the experimental version:
Step 6: click on the dropdown menu containing the text 'none".
Step 7: select the experimental version and update teardown.
See screenshot for visualisation.