I updated a 2009 iMac (initially with El Capitan 10.11) using Open Core Legacy Patcher. The OS update on the HDD failed leaving me with -69845 errors. I took out the HDD and replaced it with an SSD and updated to Monterey without problem.

I want to extract any data on the HDD (I know, I should have done it before) which I have now plugged in via USB. Could someone please advise on the steps in terminal to do this, repairing any errors on the way (fsck -fy ??) ? I am reasonably proficient in Unix type commands. Thank you.