Power Query - complicated custom column

I need to create a custom column which looks at 1 column(a), based on a trims a value from b and puts the value in c. part b: Now if the value in a does not match my criteria, then it looks at column d to find if it was the same as the previous row and if yes then puts the value of c from the previous row into the new row. Help !

Tried searching, no good

I have one part of it now: if Text.End ([SAP segment name],3) = "K09" then Text.Trim (Text.Start([Application data],35)) else ""

Need to get part b done