Assign bib numbers by going to Event setup and Assign bib numbers.
There you have a variety of different ordering options.
You can sort by:
You can assign both genders or split male and female.
The most commonly used ways to assign bibs are to assign for the entire event or by distance. You simply just enter the next bib no. you wish to start with and then press assign.
If you made a mistake and need to do it all over again, you can clear race numbers using the button in the top right corner.