Go to File open window and select the drawing you want to relink (don't open the drawing, just select it). Now click on references. In the next pop up window, click then double click or ctrl + click on the part file name and then browse to the correct part. Click OK and finally open the drawing, check and save it.
Alternatively I right clicked the broken model view and clicked open part and then it prompted me to find the part, which I did. Clicked ok and nothing changed. Closed the drawing opened the drawing and in the file tree right clicked show view and it was back.