How do i change from "Primary" column

[BadChough]

I am using phpmyadmin version 4.1.14.6 as part of my 1&1 package. I have created a MySQL table with various columns including one called "username". When I try to insert an entry that duplicates an existing entry I get the error message "#1062 - Duplicate entry 'smiffy' for key 'username'.
Well, yes, there is the same username in a different record. But that's normal, isn't it? What do I need to do to enable the column to contain the same entry in two or more records? Is this to do with "Primary", "Unique" etc? They used to use radio buttons to select them, but with this version I can't understand how to make the changes.
I've asked 1&1 Technical folk, but they couldn't help.
Can you, please?

 

[BadChough]

Apologies. I think I may have posted this on the wrong forum? I guess it should be on MySQL forum.

 

[BadChough]

Sorted.
I didn't have Auto Increment selected for the "pk" column.