To use floating point all values have to be floating point.
Move your values (whatever they are) to DMs. Be careful if you are using a constant - use &1234 not #1234 or you will get an incorrect number. & is decimal, # is BCD/HEX.
If the values are in one word then use the FLT instruction to float the value, if in 2 words use FLTL (long). Be careful as floating point takes up 2 words so watch your boundaries. Then use *F for multiply, /F for divide, +F for add and -F for subtract.
You can then use FIX (1 word result) or FIXL (2 word result) to convert the value back to an integer.
I use this method all the time for calculating values received from Caterpillar engines (CAB bus J1939 protocol via Modbus RTU).
By the way, FIX and FIXL will truncate the decimal point of course.