There are two ways. You can use the capture tab or the shiny egg tab.
If you're using the Capture Tab, select Method 5 (Standard) as your Method & Gift Pokemon as your Encounter Type. Choose which IVs you'd like & search for a seed. When you find a seed you like, right click on it & copy the full seed to your clipboard. Go over to the main window of RNG reporter. Select BW or BW (International) depending on which parents you have. In the seed hex box paste the seed you just copied. Click on the calculate initial PID frame & hit generate. It'll give you a list of possible natures to choose from when you try to hit your seed. To get the nature you desire you'll have to advance the PID frame.
If you're using the Shiny Egg Tab, set it up as you would trying to look for shiny seed. Select BW (International) as your Breeding type, but make sure your parents come from the same country. There's a good chance the egg with come out as non shiny.
If you're using the Capture Tab, select Method 5 (Standard) as your Method & Gift Pokemon as your Encounter Type. Choose which IVs you'd like & search for a seed. When you find a seed you like, right click on it & copy the full seed to your clipboard. Go over to the main window of RNG reporter. Select BW or BW (International) depending on which parents you have. In the seed hex box paste the seed you just copied. Click on the calculate initial PID frame & hit generate. It'll give you a list of possible natures to choose from when you try to hit your seed. To get the nature you desire you'll have to advance the PID frame.
If you're using the Shiny Egg Tab, set it up as you would trying to look for shiny seed. Select BW (International) as your Breeding type, but make sure your parents come from the same country. There's a good chance the egg with come out as non shiny.