This is an assembly language problem.
I already figured out how to accept user input as a string and the convert it to integer

Multiply current sum by 10 (shift by 3 and shift by 1 position to the left then add two results together)and add new digit from the string (already converted to number by subtracting 48)

Now up until the point of overflow this would work fine, but then how does the number get split up to fit into two registers? Does it have to be divided or bit shifted? Please explain in details!