Sometimes, you can't find the original ArcMap .mxd file or Arcpro project folder which was used to publish web map.
If I want to update this web map, I must have that file. It should be in someone's hard drive. But that hard drive is not available due to that person is gone.
Since I can't find it, I still can restore it through web map.
Step 1. download portal item file
Step 2. open portal item file with arcgis pro. Layer's source point to arcgis server's rest service api.
Step 3. re-set layer's data source to SQL server
Step 4. Now I successfully restore the original ArcGis pro file. It re-store all the symbol color, I can update it and re-publish it.