To ensure Market Segment field from Lead is copied to converted Account record in routinemanner without manual intervention , an administrator should ensure Market Segment field on Lead is mapped to right field on Account using Lead Field Mapping tool under Lead Settings. This tool allows mapping custom fields from Lead object to custom fieldson Account , Contact , or Opportunity objects so that data is transferred when leads are converted . For example , an administrator can map Market Segment field on Lead to Market Segment field on Account using this tool . Ensuring Account has a field thathas same name as new Lead field , writing validation rule , or writing record-triggered flow are not necessary for copying custom fields from Lead to Account . References : https :// help . salesforce . com / s / articleView ? id = sf . leads_custom_field_mapping . htm & type = 5