1. Update the plug-in: Visit the official website of the plug-in developer or other reliable download channels to check whether there is an updated version of the plug-in and download and install the latest version.

2. Disable signature verification: In SketchUp software, open the preferences under the window menu, select the extension manager tab, find the plug-in to be used on the right, and uncheck the "Enable digital signature verification" check box in front of it.

3. Install certificate: If you are sure that the plug-in is from a trusted source, you can try to install its digital certificate manually. The specific operation mode depends on different operating systems and browser types. Please refer to relevant documents for setting.