Base Editor and disappear markers

[TKDGUY23]

Dear Devs,
     I decided to add some fish to one of my base rooms in the waterway that I have.  So clicked on the school of fish, and a single fish to place them but they weren't how I wanted them.   The placement marker isn't appearing for me to delete them, and even tried the Ctrl + Z command that didn't work either it just undoes all the previous landscape stuff.