Remove Disk 1 and then Disk 2 from the array using SnapRAID's suggestion:
https://www.snapraid.it/faq#remdatadisk
To remove a data disk from the array do:
- Change in the configuration file the related "disk" option to point to an empty directory
- Remove from the configuration file any "content" option pointing to such disk
- Run a "sync" command with the "-E, --force-empty" option:
snapraid sync -E
The "-E" option tells at SnapRAID to proceed even when detecting an empty disk. When the "sync" command terminates, remove the "disk" option from the configuration file. Your array is now without any reference to the removed disk.
Then add the new disk as d1 (it's ok to not have a 'd2' entry) with your consolidated data on it.
Then perform a new sync.
It will likely take as long as a fresh sync, so you may just want to start from scratch. At least I would. One time parity generation and you're back in business.