All PKDM Baleno variants come with a trimpot adjustment to set the air fuel ratio.
Its a sort of variable resistor with a knob whican can be rotated to change the amount of current to be passed on certain points which will further control the supply of fuels through injectors.
Other cars of same era like corolla and civic also had the same way to adjust AFR instead of getting data from multiple o2 sensors.
If u think that nobody fiddled with this trimpot which can be found tucked in wiring under the steering colum of car, then no need to chanage it.
Other wise u need to take ur car to someone having exhaust gas analyser and then adjust the AFR according to optimal reasing on analyser,
There are certain ohter ways to set the AFR, you can search the indonasian. malaysian groups and channels on UPS to adjust afr by using a multimeter and asjusting the afr.
hope it helps