The 2 GPU's are already removed from your account and put against your reservation.

If only NRT-ICN both ways clears then you will need to call United after the trip is over and request the two GPU's be put back into your account. This is "supposed" to happen automatically but I've never waited long enough for it to.

GPU's are only considered used when they clear an upgrade on a flight that does not have CPU eligibility. NRT-ICN is CPU eligible so they are not considered "used".

If both NRT-IAH flights do not clear then you can get your GPU's back.

Enjoy.

-RM