Ah, I had a little study about mileage correction before. You can even do it yourself if you have knowledge and money. First, buy a correction device such as Tacho Pro. There are 4 methods, different cars need different methods, ranging from easiest to hardest
-OBD2/CANBUS interface (very little cars have these, mostly is VW and some Europe cars)
-Odometer interface (plug in the corrector to the odometer. requires dismantling from the console)
-Odometer EEPROM (need to dismantle the odometer itself. hook data lines to the EEPROM for erase/rewrite)
-Odometer processor (some cars have EEPROM build into the processor itself as SoC. needs to desolder the processor, custom make socket to connect to corrector for rewrite)

BMW have one of the most sophisticated tamper-proof system. Even if you manage to tamper with odometer, there are at least 2 more records, one in ECU and another in TCU. If their checksum don't match, the odometer itself will light up to tell that reading has been tempered. Second hand sellers either cover the light or break the connection of the LED. Not sure Proton has any of these but don't look down on Proton's ECU, they may have sophisticated things than you expect.

I'm sure if you ask some dealers or workshops, they have ways to correct Saga's mileage but if the new owner wants to check whether it has been tempered or not, it's not difficult.