You just need to write a query that combines the data of two table tables and show it as datasource of your grid.
There is other wya to retrieve both tables separately on front end and then combine - but I would not suggest this as it would be much easier to combine them at DB level.
Sample:
SELECT
t1.col1, t1.col2, t2.col3
FROM
table1 t1
INNER JOIN
table2 t2
ON t1.RegNO = t2.RegNO
Result set would have combined data that can directly be set as source for grid.