This dua is as follows:
اللَّهُمَّ أَنْتَ حَسَّنْتَ خَلْقِي فَحَسِّنْ خُلُقِي
Allahuma anta hassan’ta khalqee, fa hassin li khulaqee
“O Allah, just as You have made my external features beautiful, make my character beautiful as well”. (An-Nisai)
This dua is about character that will include behavior, manners and interpersonal skills. If a person develops good behavior, it makes things so much better at family, professional and social level.