Hi! I guess you have a blueprint for you ship that contains the thrusters lights. All depends what component you have used for your thrusters. Presuming you used point light components you can set up your event tick (I used the event tick for simplicity but the better way is to put it on the event/function you use to change the speed) in this way:
If you are using a Material with emissive channel is pretty more complicated to explain.
Have a nice day!