This was nontrivial for me to figure out as well. On the dashboard, the first box is your calendar/dataset. First make sure you've gone through and edited your races to check the Race box.
The second box (vertically) shows your statistics by default, but contains tabs along the top for STATISTICS | ANALYSIS | RACE RESULTS | .... Click on the latter, then on "All race results" (next to "Personal bests"). Here you can edit your races to add names, check the box for "Officially measured," add the official distance and time, and even include your overall, gender, and age results. (Having maintained a spreadsheet with these very data for many years before Runalyze, I find this very handy. Though, an extra box or two for links to official results and/or personal notes would be nice.)
These race-specific details are (thankfully) stored separately from the activity data, and the edit form even indicates to which activity the race is linked. I verified that the original data are intact.