Here is the excel formula with steps:

=NORMSDIST((NORMSINV(0.02)+NORMSINV(0.999)×SQRT(0.1))/SQRT(1−0.1))

=NORMSDIST((−2.054+3.09×SQRT(0.1))/SQRT(1−0.1))

=NORMSDIST(-1.135)

=12.8%

They keep changing the names of the function - e.g., NORMSDIST is NORM.S.DIST(-1.135,TRUE)in the recent versions, and same for NORMSINV = NORM.S.INV