In order to filter a Timeline, you first need to be on the Timeline screen. You can navigate there by either going to the main menu and selecting Insights and opening up the Timeline or by selecting the top three dots in the top right corner of the Points screen (as seen here).

You can filter Timeline to see everything recorded for a specific behavior, student, or teacher, or show only merits, demerits, or rewards.

You can also combine filters, to see every reward purchased in a specific teacher's classroom.

Just click on the heading of the column for what you'd like to filter. You can add multiple filters to the same column too.