Share your experience!
Translation via Google Translate:
I have a problem after updating the Android 8.0.0 system I can not find where you can set up a sms notification alert where to choose a melody, there is a standard ringing sms I can not hear it
У меня проблема, после обновления системы Android 8.0.0 не могу найти где можно настроить мелодию уведомления смс где выбрать мелодию, стоит стандартный звоноз смс иия его не слышу
Hi @Viola-kiska, welcome to our forum!
Your question has been translated to English as this is an International forum.
To change the notification tone for an incoming text message, follow the instructions below.
I hope that helps! 
Having followed your instructions on my Xperia XA1, I have found messaging and selected it.
But that's where the instructions cease to be of any use as there is no "sound" option to select!
I've succeeded in changing my alert tone for other apps, like the one for Xperia companion when I plug in to my PC, but no option for selecting a custom tone for messaging.
If the XA1 was a decent handset, I probably wouldn't be so annoyed, but I'm turning the air blue here, just trying to change my text alert tone!!!!
Try the following:
Open Messages (from home screen or from apps menu)
Tap on 3 dots on top right corner
Tap on Settings
Tap on Notifications
Is Sound option there?
No, just options for delivery reports and message read reports.
Translation via Google Translate:
I can not configure the sound of SMS messages after the update! Only for notifications of mail, the calendar gives you to set up.
У меня после обновления невозможно настроить звук смс сообщений! Только для уведомлений почты, календаря даёт настроить.
Hi again @Bohicanoid, sorry for my late reply.
I have attached two screen shots taken from Settings > Apps & notifications > App-info > Messaging, tap the red circled text!
Here you should be able to change the notification tone that is played when you receive a text message!
@Катя11, please see the post above! 
I hope that helps and sorry for my somewhat unclear instructions previously!
Translation via Google Translate:
Thank you! Everything worked out!
Спасибо! Всё получилось!
Thanks Jonas, my issue is solved!
Your instructions were very clear in both cases, but the solution you posted didn't apply until I updated my phone, I really wish I'd gone with a Samsung, the Z3c was the best phone I've ever had, but the XA1 is an unreliable, and dumber, version of the Z3.
@Катя11, you're very welcome! 
@Bohicanoid, I see! 
The instructions are a bit easier in Android 7.0 as you can do it directly from the application via the three dots in the top right corner and you don't have to venture so far into the Settings menu of the device.
Regarding your Xperia XA1, what kind of unexpected behavior are you experiencing? Please let me know and I'll do my best to assist you! 