How to translate a variable to a user for "Asignee field"

[Vogel_ Steve]

I have a question on automation.

I’m trying to set a manually triggered automation to create subtasks.

I need to set the subtask assignee based on the user selecting an "organization" rather than a specific user.

Here is my example flow:

Manual trigger – require user input : “field name” = “Assign to” selection option “validation” (only 1 for my test)

Then

Create new sub-task: need it to be assigned to a specific user (i.e the predefined user for "validation"). 

Can’t seem to figure out how to “translate” the field name value of “validation” to a user ID for the assignee field.

I tried creating a variable and using a look up table to no avail…

Any help would be appreciated,

[Vogel_ Steve]

And yes, I can accomplish this with branching but I want to be able to change assignee mappings easily (i.e in one place).