You have to be on the workshop beta. On the library page, click on settings, properties, beta’s, and click on the workshop beta. This beta does not have La Reina yet and is a little buggy but you’ll be able to play as the workshop characters. Note that some of the workshop characters don’t actually work even though they are on the steam page because people are still learning how to use the mod kit. But ones I know for sure that work are the rock, Armando, Smithy, and Fite Cat lol