Problem for deleting the drop down icon box

[aleman]

Dear All,
Encl pls find print screen which the drop down icon exist in my file.
I have no idea how it's come up as I did not set up any validation or drop down list.


I have tried delete the row that appear those box. After I delete the row, it's still exist in another row. I also try to find in Google to find some solution but still no chance to get rid of it.
Any expert can help, tks in advance.