Hi @opsilon_production! Welcome to the community. 
As the others here have pointed out, the most straightforward way to fix this particular issue is to connect to your database with a GUI tool, find the offending record, and manually fix the conflict. The other option is to use some other field that uniquely identifies the record, assuming one exists, when writing the update query:
In the longer term, I would strongly recommend ensuring that you properly set a primary key and necessary validations on your database tables! Doing so would prevent issues like this in the future.
Let me know if you have any questions about how to do any of this. 