I don't have a "300" but on the PRO96 you go to the Edacs system, press "PGM" then "TRUNK", then i think its Func-5 or F+ one of the key #'s and it goes to the next setting...On the GRE500 its done in the "GLOB" menu....
Welcome to Radioreference and Merry Christmas, hazuki!
On page 52 of the manual: "You can enter either a decimal or AFS code for ED (EDACS) IDs. The default
setting is decimal ID entry. When you press FUNC then 2, AFS Format appears
for about 2 seconds. Now you can enter the ID code with AFS format."