To add/remove a page number, click the Colors tab from the left menu, then, select Edit Theme . Next, choose the Footer tab. Turn Show Page Number > ON/OFF. Then, select Apply Changes To Presentations to save.
By default, your page number will appear on the bottom right of the footer. You can change the position to the left by clicking on Edit Footer . Then, switch Logo Position to Logo on Right. Now, your page number will appear on the left side.