1. Step 1: Open AutoCAD, select the "Tools" option in the toolbar, as shown below, and enter the following steps.

2. Step 2: After performing the above operations, select the [Load Application] option, as shown below, and enter the following steps.

3. Step 3: After the above operations, select the source design plug-in to be loaded and click, as shown below, to enter the following steps.

4. Step 4: After completing the above operations, click the [Load] button, as shown below, and enter the following steps.

5. Step 5: After completing the above operations, the word "Success" appears in the lower left corner of the window, indicating that it has been loaded, as shown in the following figure. In this way, the problem is solved.