If you add people and start a new dm on slack do you lose all of your previous messages

Carlos, an algebra teacher, is creating a series of powerpoint presentations to use during class lectures. after writing, formatting, and stylizing the first presentation, he would like to begin writing the next presentation. he plans to insert all-new content, but he wants to have the same formatting and style as in the first one. what would be the most efficient way for carlos to begin creating the new presentation? going under the file tab and opening the first presentation, deleting all content from each page, and adding new content going under the file tab and clicking on new in the left pane, then choosing new from existing going under the design tab and clicking on themes, then selecting the theme that was used for the first template going under the design tab and opening the template that was created for the first presentation