open your contact app, search that option  . copy the file to your pc 

Yes can do ota back again. Btw what firmware stock rom did you download? My s3m back in the box .

Correct firmware . Not so many function will be added to s3m even though we have 4.2, most features will go to flagship phones

My bad . Its import/export. To backup use export and restore import

yes, you need pc odin to flash the stock rom, the guide to use pc odin should be same

no need  . just install the triangle away apk

pda

that step, you need to boot to recovery mode, volume up+home button+power button

you try booting to download mode or recovery?

Check if you succeded flash it? try booting to recovery mode again, the menu will be different <3e> mode 

Check if you succeded flash it? try booting to recovery mode again, the menu will be different <3e> mode 

ok now check the binary count after using the triangle away, boot to download mode see if its state binary download 0 and current binary is official

yes,

after you finish, try check
1. setting status, make sure it state normal/official
2. boot to download mode, check again if the binari download = no, current binary = official and system status is = offical/normal

from setting or download mode? the last step to clean that is boot to download mode, do factory reset/wipe data the do the wipe cache, this should get rid the "custom"

don't forget wipe cache

don't forget wipe cache

you didn't do it on one go?