Yodakitty

I did an initial backup to Time Machine using "My Passport" when I upgraded my 2013 iMac desktop from Yosemite to Catalina a couple months ago. Subsequently I haven't been able to back up at all. I did receive a helpful reply to Yodakitty and kept it on my desktop for my son to review it but recently lost it. Can someone address my problem and help me to continue to back up to "My Passport." I hope my original backup has not been lost.