I know it sucks but doing anything besides reinstalling your OS is likely to cause massive problems.
In fact, to do it right, partition your 1TB drive move all data you wish to keep over to the new partition (especially games) and nuke the partition that used to contain your OS. Expand the created partition to include the whole drive after that.
And THEN reinstall your OS on the SSD with the 1 TB not plugged in.
and finally, plug the 1tb drive in and migrate any saves and restore backups to where they need to be.