Hi @chloecan, thanks for your post, and sorry for no reply on this yet. At the moment, the ability to alternate rows like that is a not a built in dynamic list feature, but you can create this manually, by using multiple dynamic lists and then limiting the number of rows for each dynamic list.
You can then create different layouts for each dynamic list. i.e. take a look at this screenshot, of alternating content with the each list limited to 3 items. In my example, the first list is limited by items 1-3 and the second list would be limited to items 4 to 6.