How to pass a value from a dropdown list to a column name given to the return value of a lookup?

[kasun_charitha]

As the return value of the lookup command, how do we give the value of a field in our main form?

table 1 (main form)
ID
Road Name (enum = 165,263,157,168)
layer description (this field enum = ABC, Subgrade, Subbase)
layer des. No

table 2 (hidden data)
ID
Road Name (enum = 165,263,157,168)
ABC
Subgrade
Subbase

This is what I want.
First select the road name in table 1. Second, select the layer description. Then in the table 2 corresponding to the road name, in table 2 which matches the layer description in table 1, the value should be passed to “layer des. No” in table 1.

LOOKUP([Road No],"Layer names","WCO-",[Description of Layer])

This is the lookup expression I wrote. But this is not working. Can you help?