Just as each country has its own way of saying "Good morning" using their native language, people also use the phrase "Good morning" in Japan. However, to say "Good morning" in Japanese, simply say “ohayo.” Another problem I guess you are probably thinking of is how to pronounce it. In that case, you can pronounce “ohayo” like when you want to say “oh-high-yoh."
If you can do this, you are simply saying "Good morning" in Japanese. At times, you might get confused seeing other people saying “ohayo gozaimasu." They are also saying Good morning, and if you want to try this too, just pronounce it like when you want to say “oh-high-yoh go-zah-ee-moss.
Most times, when people say Good morning in Japanese, they tend to demonstrate this with a deep bow, most especially when you are greeting an older person. In Japan, people say Good Morning to other people before 10 a.m.