This is very simple. The bit weight as I like to call it is given by (range)/(2^(number of bits)) so in you case it will be 5/(2^24)=bw
If you want to create a value equal to 0.4551 volt with your DA volt. just calculate 0.4551/bw = 1527062.20032. Then write the rounded value 1527062 to your AD