This is nothing more than updating the table where date is greater than the date being passed in. The reason you are having a problem is because you have dates stored as an integer. You first have to painstakingly split that int into a usable datetime and this becomes trivial.
Update YourTable
set CardNumber = NewCardNumber
where MemberNbr = PassedInMemberNbr
and EffectiveDate >= PassedInDate
If there is ANY chance you can change this table to use the correct datatype for dates it will go a long way to making your life easier.
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