Hello,
Very simple.
Everything is almost like if the upslope of the runway was added as a downslope on the approach.
For example if the runway climbs up 1°, it's almost equivalent as if you were on a 4° approach slope.
Then, increase flare height or force accordingly.
If you flare with the same force, the flare height should be increased by the square of the ratio of the slopes (for a stabilized approach).
Also if you flare with the same height, the flare force should be increased by the same ratio.
For example, if 4° instead of 3°, increase flare height by 77%.. Or increase both force and height by 30%.
I'm not asking you to compute this inflight, but keep in mind that you're going to have a significant effect due to this squared term.