Duplicate UserForm pasted info

When I 'Submit' my userform it places the textbox entries onto a separate sheet in the first available row as intended.

What I also would like it to do is duplicate the entries if a specific field is filled out so it essentially fills in the first 2 available rows instead of just one.

What I have is a textbox named txtNew that when filled will assign a new serial number to the product identified in the form. I need to put in all the userform's info in one row under the original serial number and repeat right away with the new serial also. This is so that when searching for either serial number the user will be able to pull up record of the change.