Your question is a little light on details but from what I surmise you want to create a new field with replacing all the values with "unknown" to "Open"
This is very simple with the If() function
If(Status = 'Unknown','Open',Status) as NewStatus
You were asking about peek which will allow you to get the value from a field based on the row number you request. Keep in mind the row numbers used in peek begin with 0, your example indicates you were using a 1 as the row number. If what I have mentioned does not help please post some code so we can see what you are doing an better understand the requirements.