How can I have 1 form or field update 2 fields in 2 separate forms.

How can I have 1 form or field update 2 fields in 2 separate forms.

My ultimate goal is to have 2 form field put data into 2 fields in 2 separate forms.

Here is current code:

if (input.Completed == TRUE)
{
    lastWorked  =  Checkout  [Checkin_Date];
}

I get the following error: " Error in statement at line number 3
A Boolean expression is expected in the where clause. and but an expression of type TIMESTAMP is specified here "

I want to fetch the Checkin Date and input it into a different table.  This could happen when someone clicks the "Completed" checkbox.

What am I doing wrong?