Create a connector with bidirectional arrows
In draw.io by default, connectors have arrow heads at one end, where it connects to the target shape. You can add an arrow head at the other end via the format panel on the right.
- Select the connector.
- In the Style tab of the format panel, select the middle drop down on the second row, then select an arrow head from the list. This will add an arrow head pointing towards the source shape.