Child Theme DT 8.9

I have tried a number of times to activate a child theme

Per instructions since my WP Editor doesn’t work I FTP and change XXX to DT with out any [ ]

I can’t seem to see a place in the back end that allows you to pick which child theme to be active.

I do see all the child themes listed. I hit install and they install in my back end but then what?

In design setup it has the default one sitting (a screenshot of it)