How i can close viber sent tone

i am having difficulty regarding the customization in Ios

especially regarding the Apps tones

one of the worst operating system apple iphone is having

i want to listen only call ring

dont want to listen app calls ring (eg viber tone )

closing notification viber sound...why i m stil listning viber sent msg tone

i m using iphone 6

for business purpose iphone is at Zero level

u cannot sent ur pdf file Cv over a website....choose file only Pic

no idea why people r running behind iphone, big mistake to buy this phone

if someone is having proper answer then reply, not interested for funny replies