I found this video by fzsdjbncf2000 pretty helpful with the correct way to say konnichiwa. I myself have been guilty of pronouncing it like kon-NI-chi-wa (putting emphasis on the NI) but in fact, you do not put stress on any of the syllables in konnichiwa.

He also explains that you only usually use “konnichiwa” with your superiors, elders, or others older than you or those that you respect.  He explains that using “konnichiwa” is not normally used amongst friends or in other closer or intimate relationships.  A more common expression among friends would be “ohayoo”.

Check out the video!  Hopefully it helps with your pronunciation of konnichiwa!