Hi @Madumi ,
Do you want to create a Primary column "Full Name" within your Salespeople entity to act as the "Full Name" column in Contacts Entity (concatenated with First Name column and Last Name column)?
Based on the needs that you mentioned, I afraid that there is no way to achieve your needs in PowerApps currently. I agree with @DavidJennaway 's thought almost. You could consider create separated First Name field and Last Name field in your Salespeople entity (mark the two field as Required), and then rename the "Primary Name" field in your Salespeople entity into "Full Name".
When you create a new record in your Salespeople entity, you could consider design a Workflow to concatenate the "First Name" field value and "Last Name" field value, then populate the concatenated string value into the "Full Name" field.
If you generate a PowerApps app based on your Salespeople entity, and want to use PowerApps app to enter new record into your Salespeople entity, you could consider go to the Edit screen, then select the Edit form, then unlock the "Full Name" data card i your Edit form, set the Default property of the "Full Name" Text Input Box to following:
FirstNameTextBox.Text & " " & LastNameTextBox.Text
then when you enter first name and last name within your form, the "Full Name" field would be populated with the concatenated value automatically.
Best regards,
