Electrical Connectors

Starting my Octavia A5 1.6 Fsi has become a hit-and-miss affair and I wish to check all relevant electrical connections before deciding whether or not to replace the starter motor. However, the connector going into the starter solenoid housing is unlike any of the other connectors on the car. It has a red tag that slides about one centimetre forwards and back, but in neither position can I loosen the plug. I would be very grateful if someone with experience of this type of connector would tell me how to unlock the thing.

Finally, Are special tools needed to separate plugs from the wiring? I would lik to replace a connector I damaged. With thanks in anticipation. Ned