Thank you for sharing your query. We would like to inform you that Samsung neither recommend nor provides downgrading procedure of OS in device after an update. You can only update your device using smart switch or FOTA. Be sure to hit ♡ when you find an answer that works for you.
For Further assistance, you can get in touch with us via Live Chat option by following- http://livechat.support.samsung.com/Customer_new/IN. You can also connect us via Samsung Members web community by following mentioned url-https://community.samsungmembers.com/en_IN#/
use this link https://www.sammobile.com/firmwares/galaxy-on5/SM-G550FY/INS/download/G550FYDDU1BQK2/196620/
and see all instructions carefully
InstructionsExtract (unzip) the firmware fileDownload Odin v3.13.1Extract Odin ZIP fileOpen Odin v3.13.1Reboot Phone in Download Mode (press and hold Home + Power + Volume Down buttons)Connect phone and wait until you get a blue sign in OdinAdd the firmware file to AP / PDAMake sure re-partition is NOT tickedClick the start button, sit back and wait few minutes
