If you want to convert U8 number N to the character which has the ASCII code equal to N (for example 65 -> "A") then you can use "Functions->String->String/Array/Path Conversion->Byte Array to String.vi".
If you want to convert number N to the string "N" (for example 65 -> "65") then you can use vis from "Functions->String->String/Number Conversion" or such function as "Functions->String->Format into String.vi"