I posted this same question about a month ago but for SP 2013. I noticed in 2010 (I have to rebuild my WF since I want it to kick-off from another workflow and this cannot be done in 2013) the variable is not just GUID like in 2013, but the only choice is List Item ID. Is the action the same concept? When I get to "Update Item in" I choose in Find the List Item -- Field: ID and Value: IrvFirstDay (the value I named to output with List Item ID as the type?)
It turns out that, YES, the concept is the same, I had the Field as ID correct, I just had my "then" statement nested incorrectly. It looks like something's missing where the space is where it says "start typing or use the insert group in the Ribbon" but moving the "then" statements down worked perfectly for me.