Replace Function need help please

[joffner]

Tried multiple ways and can't see to figure out the correct way

The below doesn't error however it's not changing the ouput, someone recommended the replace function but i can't figure that one out

if [MRP Controller] in ('F84','F85','F86','F87','F88','F89') then [System LT] = 14 else [System LT] endif

Replace([MRP Controller], 'F84', [System LT], '14')

[binuacs]

@joffner you need to write the formula under the field System LT not System LT2 

IF [MRP Controller] in ('F84','F85','F86','F87','F88','F89') Then 14, Else [System LT] EndIf

[joffner]

Thank you so much! That did the trick