If you have to change an athletes age or gender you can do this easily, however you may have to do some more steps to get their new age or gender into your events/recording sheets.
Step 1 - Edit age or gender - go to Home - Search for the athlete - click on Update for the athlete's name - edit the required field - then press Submit
Step 2 - to make sure your athlete makes it into their new age/gender events and recording sheets, follow these steps https://support.timingsolutions.com.au/hc/en-us/articles/115005418546-Missing-Athlete-s-from-results-entry-and-recording-sheets
Step 3 - if an athlete is still in both their previous and current age/gender events you will need to do this and then repeat step 2 above.
Now that all the events have been deleted, go back to step 2 above and re-nominate the athlete into this date.