To set the sport level to a client look for the client on Client -> Clients.
Once there click on to enter the client's file
Then go to the section Game Information in the client's file and click on the Game Level tab
Here you can select the sport to set the level and click on the checkbox if the client is federated on that sport, and also set his/her position in the ranking manually.
To set the level press under the information section
Once you're done click on Update to save the changes