You can move or copy fields from one part of a client record to another using the field reference.
N.b. it is not possible to copy fields between the Contact details form and the Client details form.
Creating a copy of a field
1. Go to Settings > Forms and select the Edit client form.
2. Find the field you want to move, and copy the field reference. If there is no field reference present, you can add one and then copy it.
3. Add a new field to the part of the Edit client form where you want the copied field to be.
4. Give the field the same name, and paste in the field reference that you copied in step 2.
5. Save the form. You will now see that the same data entered in the original field will be present in both fields on your client records.
Once you have done this, you can then go to the Edit client form settings once more, and delete the original field from the form setup. This process effectively moves a field from one part of a client record to another. You can also keep the original field, if you want this field to appear in 2 places.