Manipulating values in Grid

Hello, i created form with grid which have values from some table "A".


Table A have 3 field.

When the user will be enetering values into field 1 in grid i want to automaticly insert values in field 3 depends on value 1. How should i do that? I tried with method modified on the first field but don't really know how to set values. I already have values from field 1 and with them i'm finding in other table data which i want to assing.


Thanks for your help!!


This is how i create new records