how to Copy value from sil field to single select dropdown field in the same screen

[Jeya]

We have requirement :

1. In the create screen we are changing app id to app name using sql(datasourceName, sqlstring, [...]) this syntax.

2. we would like to copy this app name field value to single select drop down custom field in the same create screen.(either through postfunction or automation) whatever possible method

[Jeya]

for the select dropdown field value is coming up when we put runner log, the problem is filed itself gone from the  screen not getting set in the screen .