Less automatically stores all the previous versions of your models. In other words, every time a team member saves a model, a new version of that model is created automatically.
Read more about versions here: Versions, Draft and Publish
Go to the folder with your model and click on the three dots to the right-hand side on the row. Click Version History.
From there you can see the currently published version (1 below) as well as the last 20 other versions (2 and 3 below).
You can click on the currently published version to open it up in a new browser window. You can also publish a different version or open it in a new browser window via the three dots on the right-hand side of each version.
If you change the published version, that version will become the scheduled model.