To add a map to your existing topic, first make sure you've locked in your mapping location. In the Management Dashboard, select the the Settings tab, then Location Settings. Unlock the existing map and zoom in until you've landed on your project location - then lock in the location and select Save. From here, you will navigate back to the Management Dashboard and click the Topics tab as shown below.
Choose the topic you want to add a map to by clicking the gray "Edit" button on the righthand side of the Topics page as shown above.
Once you're directed to your editing topic page with a header as shown below, scroll down to the Media header.
This section provides you with many media options to add to your topic, one being a map. The screenshot below shows this "Media" section; the first option is to add a map to your topic-- check the "Enable Map" box. If you have any KML layers to apply to the map, you can upload those under "KML Map Layers".