MySQL error code 1175 during UPDATE in MySQL Workbench

Question

I'm attempting to insert the number 1 into the previously visited column. I'm composing the statement in the SQL editor within MySQL Workbench while using it. I'm typing the command below:

UPDATE tablename SET columnname=1;

It gives me the following error:

You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column To disable safe mode, toggle the option ....

I did as instructed and deselected the safe update checkbox under Edit > Preferences > SQL Editor. The same problem keeps coming up and I can't edit this value. Tell me what's wrong, please.