Make a backup of your project before following this guide.

Go to the S_BuildPartInfo and copy the video below.

Next go to the BuildPreview blueprint, Compile it then copy the video below.

Add the highlighted nodes shown in the image below, location at the top of the image.

Next go to the BP_MasterBuildPart and copy the video below.

Next go to the BP_InventorySaveSystem and create a new variable called BuildPartIndex and set its type to Integer.

Then create another variable called LoadedBuildPart and set its type to S_BuildingSave.

Then in the Event Graph copy the video below.