You can do it 2 ways:
Make a tone search. Navigate to the channel you want to apply the search to, and press MODE until either CT: Code Search or DC: Code Search appears. When it finds the tone when a user transmits, press ENT, and it will store the tone.
Enter manually. Navigate to the channel you want to store the tone for, press PROG, and press MODE until either CT: Code Search or DC: Code Search appears. Then press FUNC + MODE, and enter your tone on the keypad and then press ENT.