Hi Gopi,
May I know what the control that you used here?
A custom Gallery, or something else?
Lookup function would require the condition in the following format:
Lookup(Table, and(Tablecolumn1=Value1, Tablecolumn2=Value2), ResultColumn)
Based on the description and my understanding, I suspect the formula should be:
Lookup('[dbo.Customer_Master]', and(Sales_Org=[Value Input for SALES_ORGANIZATION_ID],
Distribution_Channel=[value Input for DISTRIBUTION_CHANNEL_CDE]),CUSTOMER_NM)
For the Value input, that depends on what control or Input Method that used.
Please share more details regarding the gallery, so I could make some test from my side and share the results out.
Regards