How to change the speed of an engine through a script?

Hello! I Speak Spanish... And I need Help

1. I have 1 block in the "WorkSpace" with an engine

2. and another block above the engine

What I need is

¿How do I change the engine speed by a script?

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My Script

game.Workspace.Motor.FrontSurfaceInput.LeftParamB = 1.0

Output Print

16:52:03.937 - EnumItem cannot be modified

How can I do it?