There doesn't appear to be an easy way to add a new index by selecting from existing columns? (in the indices tab)
You have to manually type the field name.
I haven't tried it yet but it looks like I could go to the columns tab, check unique index, then edit the resulting script
and execute the script...
Non starter, I edited the script to remove unique, click execute, the dialog goes away.
Reopen the table for modifying and the new index is there and unique. So editing the script is possible but does nothing - if it's read only, it shouldn't be editable.
So in summary, there's no way to pick a column to create a non-unique index. It might seem minor to have to type the field in but other tools do this better.