Action query with a pulldown list

Hello people,

First time I am visiting this page. My name is Edmundo and not a very frequent access user. I have a question, maybe a stupid one for experts like you, but I hope someone can help me out.
I want to execute an action query an a table to update data. I have created a form with a pulldown menu (PROJECTION) and an execute button to activate the action query. When I select a value from this pulldown menu and press on the execute botton I want the action query to update the table with the value from the pulldown menu. However, the query keep asking for parameters and doesn't update the table.

My form pulldown table is called PROJECTION with a field called PROJECTION_ID (the field containing the values to be updated)
The table to be updated is called: MAINTABEL (with a field called PROJECTION_ID)

Can anyone tell me what command I have to fill in the fields 'criteria' and 'update to'...??

Hope anyone can give me some help. I would appreciate that a lot and thank you in advance.

Regards,

Edmundo