In Microsoft Excel, you can find the "Create Sparklines" dialog box in the "Insert" tab.
To access the "Insert" tab, first open a new or existing spreadsheet in Excel. Then, look for the "Insert" tab on the ribbon at the top of the window. Click on this tab to reveal the options for inserting different types of content into the spreadsheet, including sparklines.
In the "Insert" tab, you will see a group of icons for inserting various types of content, such as tables, charts, and shapes. One of these icons is the "Sparklines" icon, which looks like a line chart with a spark symbol. Clicking on this icon will open the "Create Sparklines" dialog box, where you can choose the options for creating and formatting your sparklines.