If the incoming value for a number with a suffix is in the wrong text casing (perhaps because the 'Proper' Text Casing option has also been selected), you can apply the following Regular Expression (RegEx) Data Transformation that looks to see identify the suffix after a number and seeks to change it to a lower case.
(?<=\s\d+)(St)+
(?<=\s\d+)(Nd)+
(?<=\s\d+)(Rd)+
(?<=\s\d+)(Th)+
If the incoming value has the suffixes being in all caps, then the RegEx will look like this:
(?<=\s\d+)(ST)+
(?<=\s\d+)(ND)+
(?<=\s\d+)(RD)+
(?<=\s\d+)(TH)+