Tutorial references a button that does not exist in the UI
The beginner tutorial appears to reference a button that does not exist when prompting the user to edit the Mirror effect.
The step says "To the right of the Reflection Center, click on the box with a target icon inside". There are no buttons to the right of Reflection Center, just the two blue numbers indicating the position.
The animation at the top of the window seems to indicate clicking something in the Project panel instead of the Timeline, which does not look like a target icon, and does not exist in the UI either anyway.

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Matias Bolyos commented
The tutorial is incomplete indeed.
You can find said button under Effect -> Effect Controls (F3)
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Faisal Kabir commented
same issue here.
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Bruno Quintin commented
Hit f3 to open your effects panel