If you are using an x96XT scanner, one Alpha tags Radio Identification Numbers using one format, but with the x36 Home Patrol line, it is different.
On the x96XT, I set up a separate group for alpha tagging radio ids, for ease of maintaining. They don't have to be in the same group as talkgroup ids are location. Just be sure you use the "i" in front of the 6 o 7 digit radio id number (which tells the scanner a Radio ID is involved). That goes in the talkgroup column and the name you wish to associate with the Radio ID in the Alpha tag column.
On the x36 Home Patrol scanners, Radio ID information is in the System level, using the Unit IDs tab in Sentinel.
Regardless of which model radio, Radio ID data is "global" meaning it is not associated with a given talkgroup because the radio can use many different talkgroups. For example Radio ID 180010 can show up on Fire 5, Police 1 or Med 3 talkgroups.