The Editor in DJI Go 4 will stich and view them. The app I use outisde of Go4 to view them on my Ipad is Theta. There is also a Theta+ for editing but I haven't used it. Ricoh is the publisher of Theta and it's available as an Android app (which I have on my Samsung phone) and as a Windows program. For stitiching the images on my computer I use ICE that BD0G mentioned. All these apps and Windows programs are free. I'm running the programs in Windows 7.
Here are the quick instructions for stitching them in Go4 (you need to be connected to the Mavic).
From the Go4 opening screen, choose the Editor option along the bottom. On the next screen, choose Album along the top edge, then below that, Photos. Look for the photo(s) with the pano or globe symbol in the corner. Tap the marked photos to begin the stitching. When complete, use the download button in the lower left corner to save the stitched photo to the device. Look for them using the Ipad photo app.
When the photos are downloaded off the SD card to the computer, there will be folders for each of the pano/sphero photos with all the individual shots. The actual stitched photos were in the Export Works folder.