In updates and servicing allow for redownload update when something goes wrong an update
We are unable to redownload an update under updates and servicing. Sometimes an update has a problem when downloading and it gets greyed out.
There is no easy way to redownload the update and we are stuck with an update that cannot be applied anymore
What you're looking for is the Update Reset tool released in CB 1706: https://docs.microsoft.com/en-us/sccm/core/servers/manage/update-reset-tool