Customer list update

[singupalli]

hello

any ideas how to do the following

I have in Sheet1 - in Column M the names of the customers, this list is updated every time enters a new sales via the User form.

I have another sheet named "customer transaction" where i have copied the list of customers and removed the duplicates

When a new data/entry is done the data is recorded in sheet1, but the new customer i have to manually update in "Customer transaction" sheet.

is there a way the this can be recorded automatically, but before listing, needs to see if this customer is already recoded in tnis column and then update.

can this be done

anyone

thank you