As I checked the last OTA update for s9+ was released in 21 st of july(for the slk region).If you want to manually update follow this.
1.Backup your data using samsung smart switch to the sd or to an external usb drive.(This method wont wipe your device but its better to have a backup if anything goes sideways)
2.Download the latest firmware from sammobile for your model with matching csc.(you can find your csc code under Aboutphone->software info.-> service provider... its an three letter code. ex- SLK which means sri lanka)
3.download odin (The software used to flash the firmware)
4.Extract the firmware and there will be 5 files but we only want 4 from odin locate the extracted files . This is the part you can choose whether you want to fully wipe your device or not. You will see there are two files named
CSC and HOME_CSC
If you choose HOME_CSC it will not wipe your data and update as an OTA. If you choose CSC your device will be fully wiped.
After that put the device into Download mode and connect it to the computer.you should see the com port on odin.If you dont see that install samsung usb drivers.
To go to download mode - Turn off your device then press bixby key + volume down + power key at the same time.Then follow the onscreen instructions.
I highly reccomend you to watch a youtube video because its a very easy task but it may be seem very hard because the way I have instructed😅.
But dont forget these.
1.Backup 2.Download the correct firmware matching your current csc. 3.Choose the HOME_CSC if you want to keep your files and apps.