Everyone is used to seeing Pokémon GO being played in a portrait mode where it fits nice and comfortably in your hand, but sometimes you want things another way. Putting the game in landscape mode can help you see in a different view and maybe even help you see Pokémon that are further out.
Here are the steps that were found on redmondpie.com:
Step 1: Fire up Pokemon Go and turn your iPhone into landscape mode and keep it in that orientation throughout.
Step 2: Tap the Poke Ball at the bottom of the screen.
Step 3: Tap Settings in the corner of the screen.
Step 4: Scroll down and tap “Report High-Priority Issue.”
Step 5: Tap “Yes” when asked if you’re sure that is exactly what you want to do.
Step 6: Your iPhone will then be kicked out into Safari to load the Pokemon website. We don’t actually need that, so press the Home button.
Step 7: Fire Pokemon Go up one more time and marvel at its landscape-ness.