1. First, visit the official website of the plug-in developer or other reliable download channels to see if there is an updated version of the plug-in and download and install the latest version.

2. Secondly, open Preferences under the window menu in SketchUp software, 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. If it is finally determined 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.