@SJCharlesworth Go to Extensions > Sketchucation > ExtensionStore or click this icon...
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Sign into Sketchucation account if asked and click Search...
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Type in fredoscale and hit Enter and then click the Red install button
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After the Success message close the dialog and restart SketchUp
Now you will need to activate your license. You can follow this guide for that.
To retrieve your license files go to My Licenses