Refactor data export preparation to use correct indexing for DataFrame columns

app.py

@@ -242,7 +242,7 @@ with tab2:
 
         if st.button("Prepare data export", key='data_export'):
                 data_export = st.session_state.working_seed.copy()
-                for col in data_export.iloc[:, 0:9].columns:
+                for col in data_export[:, 0:9]:
                     data_export[col] = data_export[col].map(dk_id_dict)
                 st.download_button(
                     label="Export optimals set",