There are two ways to add text to your draw.io connectors. The easiest way is to select the connector and just start typing. If you want the text to start from a specific position, double-click on the connector at the point where you want the text to be, then start typing. Of course, your connector text can be formatted using the Format Panel just the same as text inside shapes. To reposition text, simply grab the orange diamond and drag it to the desired location.