Inpute & Update record in excel

Inpute & Update record in excel

I am working on creating a user form to store data in excel & update
record, I have 3 requirement to complete my user form design.
How can i create a unique reference number (preferable starting with first
3 character in some textbox followed by incremental number) for each of
the record which is getting saved in a excel using userform.
Also would like to know how can i retrieve a record and update record in
excel using userform.(Preferable by using one or two value) In case search
result have more then one record to search result option to select
required record.
I will also be adding 3 drop down box(Segment, Product & Sub Product) in
user form. Values which are available under Product should depend on what
user have selected Value under Segment & Values which are available under
Sub-Product should depend on what user have selected Value under Product
Sample structure of Database i have created in excel
Segment Product Sub-Product SEG-1 Prod-1 SubP_1 SEG-1 Prod-1 SubP_2 SEG-2
Prod_2 SubP_3 SEG-2 Prod_2 SubP_4