Need VBA code for Merge multiple column

When one customer purchase multiple products and pay all items bill in one single payment then the payment amount will be merge & center with all the products code value's row as like I display in the sale data section. Example: First I will input the date, product code, qty and hit the Add Data button. After completing all product Add Data work I put the final payment amount. Then the payment amount will be merge and center with the existing add data row value. Remark: I will complete all data entry action by using the user form. So please help me to complete the code work for the visual basic. That means Total Payment data will merge with previous sale data.

Example: Please see the attachments Merge and Center.png