If you use Macrium Reflect in "drag and drop" mode, you can drag individual partitions from the source drive (SSD) and drop them on to a partition or free space on the destination drive (HDD) and resize the partition to make it fit if necessary.
When I use this method, I usually tell Reflect to delete the existing partition on the destination drive where I'm about to drop a partition from the source drive. You can experiment, change partition sizes and only decide to commit, when you're absolutely certain you've got things right.
Does the partition you want to copy include a bootable OS or is it just a data partition? If it's bootable, you may have to copy more than one partition off the SSD on to the HDD, to make the HDD bootable, e.g. a small UEFI partition.
It's still a very good idea to backup all important data on the destination drive and probably the source drive too, before proceeding. It's easy to make a mistake and wipe important files.