Greetings fostercz,
So far you are on the right track! There are some different ways to obtain the result you seek; depending on the overall logic of the strategy. However, just by comprehending the basic concept of the BWMFI indicator, we can argue that on any given timeframe there can only be one of the four instances present while the remaining three will be absent; either MFI up Volume Up, MFI down Volume Down, MFI Up Volume Down or MFI Down Volume Up. Since the absent instances will have the value of zero and the present occurrence is going to be above the value of zero; we can use the IF block, as shown in your screenshot to proceed and apply the GREATER THAN logic. Please look at the following screenshot.