Help clearing duplicate values across columns but not deleting rows

Hello,

I have contacts on a sheet that have multiple phone numbers for each contact going across the columns on each row. Many of the numbers are duplicate and I want to clear the value of the 2nd + instance while leaving the 1st instance.

I cannot use the remove duplicate button in excel because it doesn't search horizontally and I don't want to remove any rows. Does anyone know the best way to clear the value of the cell after the 1st instance? I need it to search across the range AC2:AT6900

Thanks so much for your help

Example of file

Bold is what needs to be cleared
First Name Last name Address phone 1 phone 2 phone 3 phone 4
Mike Smith 1234 St 9999999999 8888888888 9999999999 9999999999
Peter Pan 231 Ave 6666666666 6666666666 2222222222 3333333333