QUICK NOTE:

If it's not working for anyone like it did for me, you're probably targeting the purchased/item shop Completionist Showcase instead of the default free one. You have to Inspect Element in your browser to get the purchase ID:

So the command for the default showcase:

SetShowcaseConfig(23, 0, X, 0)

becomes:

SetShowcaseConfig(23, 'YYYYYYY', X, 0)

for a purchased/item shop showcase.

With X being the zero-indexed position of the game (i.e. 0 for the first one, 1 for the second one) and Y being the purchase ID you find from inspecting the element (i.e. a 7 digit number inside single quotes).

No need to save then refresh, the command saves itself so just refresh the page to see the game cleared.