try below c# code and convert it to vb.net
foreach(DataRow row in table)
{
if(row["Column_1"]!=null and row["Column_1"].ToString()=="5")
{
row["Column_3"]=1;
}
else
{
row["Column_3"]=0;
}
}
//call AcceptChanges() to persist changes made.
table. AcceptChanges();