I want my fiance to join me in the states

My fiancé applied to come to the states about 5yrs ago from Nigeria. When he applied, his actual year of birth was miskeyed, so instead of 1979, 1970 was keyed as his D.O.B. on his passport. He was denied entry into the country at that time due to not having the need documents. He now resides in the U.K. and I would like for him to join me, how do we go about getting this fixed? Should he get his d.o.b. corrected once he get to the U.S., or would that be more difficult.

What is the application name (the application which he filled in order to get the visa)?

I applied under a visitor visa. This time we are planning to apply for the K-1 Visa.