How can i add a grey description text in add listing

Hi All,
I would like to add a small grey description text below or to the right of two of the main title heading in Add Listing, such as Title and Description in Listing Description. The small texts should appear like “Separate each keyword with a comma” shown below keywords. Try to add this in theme options, listing setup but it did not give me the effect i am looking for.

I am new to this so can someone tell me where to do the changes for this in DT the newest version with a child theme install or how are where can i go about doing this in the child them files? Thanks kindly.