The SSD is used as a cache so just ignore it. It is not for normal use. TRIM is automatically set for the SSD in Windows 7 onwards. Never defgrag an SSD it is not necessary as the method of storage and reading is totally different to the usual hard Drive. Defrag should have been automatically disabled for the SSD. Just leave it as it came.
iPhone 7 review: a range of small updates add up to an excellent phone