How to find a newly created field in Actions / Field Update when that field is located in a grid

I’ve added UDF’s before and created actions that used Navigate Parameters to write to that UDF, but in this case I am looking to update a UDF but I can’t find it when I search.  There may be a few reasons why, which I need help confirming.

1. You can’t update a UDF via Actions
2. You can’t update a UDF via Actions if it is located in a grid.  In this case its a service order details UDF.
3. I am missing some kind of Layout Properties setting which will make it accessable via Actions/Update Field.