My apologies. As I said, I wasn't sure that I was understanding your intention.
Sounds like you need to have a number of text captions or Smart Shapes hidden on the slide where you want the content to appear. These objects will contain the relevant information corresponding to a given day. But you set all those objects to occupy the same space on the slide, one on top of the other, and you set their Visible in Output value to OFF (so that they will be initially invisible to the learner) and group them. Making them into a group just makes it easier to HIDE them all with a single action line.
When your user clicks one of the buttons at the bottom that corresponds to a given day, that button could just execute a Standard action that has two action lines. The first line should HIDE the group, (so that any objects made visible from previous button clicks are immediately hidden) and then SHOW the specific caption or smart shape that corresponds to the day the user clicked.
Unless you intend doing something else with the variable, there's no need to have a variable set to any value just to achieve the interaction I have described above. However, if you DO later need to know which day the user clicked on (perhaps to use it in some Conditional Action) then you can add a line action that assigns the variable value.
Is that closer to what you want?