The Fusion Drive should display in Disk Utility as a whole drive, but it split according to the pictures you post. Then, the first step you should take is to recover Fusion Drive files and then repair the drive.
As the iMac is still bootable, you can run iBoysoft Data Recovery in macOS recovery mode to save your Fusion Drive files. Running Terminal commands to launch this data recovery software and scan the Fusion Drive for lost files.
After you have recovered data from the drive, you can go on creating the Fusion Drive again on Mac by running Terminal commands in macOS recovery mode, this process will delete all drive data, make sure you have already recovered the wanted files first.
Here's a detailed post: How to Fix A Split Fusion Drive on iMac And Recover Data?
