Update (Was in drafts for a few days, sorry) Looks like I got it figured out. Not sure if it what I did was the right approach, but it rebuilt successfully.
Found it hard to modify\append the racerx value in the username_lower column using the syntax so I went about it another way. by looking up the IDs for the rows and modifiying the username_lower value in a specific row.
First I tried to get a report of any rows in the users table that had “racerx” in the username_lower column.
select all from users where username_lower ='racerx';
From this I decided I’d modify racerx to racerx2, I can’t remember exactly what I typed to make that happen. I think it was UPDATE SET from users username_lower racerx to racerx2