This is a common Servo service. All simple Servos need to attach to a ServoController. Currently, the list of ServoControllers are :
The Servo needs a controller in order to operate. You should be able to select one in the drop down. Select the correct signal pin the servo is attached to. Then select "attach" and the servo should be controllable with the slider bar. Limits can be set in order to protect the servo from going beyon a certain minimum and maximum value.
Now there is an additional method Servo.setSpeed(0.5). At the moment this is only accessable through Python. This will set the speed of a servo. The servo will remember it's last speed until it is changed again. Valid values for speed are between 0.0 and 1.0