Hello!
There are many ways to address the last rank of a selection, depending on what your goals are.
For example, if you want to apply a trigger to the last ranked selection, you choose "Probable Loser" in the "Selections" field of the trigger, because the selection with the highest odds is called "Loser" in MarketFeeder Pro (of course, it can eventually become winner).
If you want to check some property of the loser in your trigger condition, you can just start with "Probable Loser's". For example:
Probable Loser's Back Price is less than 100
Also, the rank of the loser is in fact equal to the number of selections in the market, which is stored in the runner_number variable, so you can use that too. If you need help with adjusting a particular trigger, just attach it here.