The phrase "to select a theme" means to choose a specific topic or subject that will be the main focus or idea for a particular event, project, or creative work. Full definition
The first important step is to select a theme for your baby shower, as this can influence everything from the food to the games. (pregnancy-info.net)
Do not be afraid to experiment with your resume but make sure to select the theme of your design according to the position, industry and company. (resumesamples2017.com)
The journal is published six times a year including special issues on selected themes. (jstor.org)