If you click the ‘Advanced’ button underneath the lessons section, it will take you to a page which shows you all your remaining lessons. From there you can select whichever content you’d like then click ‘Begin lesson’.
For reviews though, you don’t have any choice over what you review and when because that’s the point of WaniKani’s SRS system. You will be shown items to review at time intervals just as you’re about to forget them. You can read more about the time intervals in part 4 of this post.