The initial draw is done in software; it can then be modified by hand to resolve any clashes that might remain.
I've select Race 40. On the left hand side of the screen you can see all of the races it is linked to. Race 43 (where same the boat is being used) is shown in red, since it is less than 35 minutes away.
To resolve this, drag & drop the race to a new time.
The race will be shown in red (to clearly mark which race you have moved), and all races renumbered & retimed as appropriate.