This question usually arises with windows 10 non-admin users, but if your using DISM I have to presume you are an admin and have enabled users OS rights etc, In which case there are a few suggestions.
There are 3 methods listed here https://www.sumatrapdfreader.org/docs/Setting-Sumatra-as-default-PDF-reader.html
I had no problems on Windows prior to 10 as an admin user in selecting make as default in the SumatraPDF menu > settings > options, UNLESS I FORGOT to check Don’t ask me again
In Windows 10 that request seems to be OVERRIDDEN as EDGE protection instantly redirects it back ! which I suspect is what your are having problems with.
So you would need to try the second method, however that does not always cut it so you could jump straight to the third
The known way to force edge not to reset pdf handling back to itself (apart from uninstalling 10, which was my first choice on 2 out of 4 pcs) as described at the end of the linked guide above is you need to go to Windows Settings > Default app settings > Choose default applications by file type (NOT Set defaults by app) and change it as shown here