There are two options, how to downgrade from EURO5/EURO4 to EURO3. (Disable AdBlue system)
 
1: With VEDOC code and XENTRY
Calculate  DAS password and VEDOC code with VEI device.
In DAS Xentry choose Downgrade official procedure.
Video is here: https://www.youtube.com/watch?v=wDuCS3ffj_o
Note: some trucks DAS Xentry not supports, and flash files are online in XENTRY database.
 
2: Rewrite PLD flash file.
In our database: http://autovei.com/en/dump
Choose a PLD type you have (A1, A2..), Engine model, and EURO III
From https://my.autovei.com download a flash file you need. (Only for VEI users, with limit 5 files per day)
Make backup of your flash / eeprom before any operations.
Write new flash file, and after original EEPROM.
To disable Adblue light on dashboard, go to XENTRY and turn ADBLUE light OFF (INS, FR module).
Do not forget to check IMMO and keys status, if truck not start.