pretty sure you will not be the last   download a rescue/live linux like system rescue cd (i used a "older" version 6.0.3, mdadm and lvm worked ootb, any newer should be fine too), transfer it to a usb (not your dsm boot usb) to boot from it assemble your raid1 system partition like here (1st partitions of all disks as /dev/md0) skip anything about swap or volume1 data partition, we only need access to the dsm system partiton https://xpenology.com/forum/topic/7004-tutorial
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