So you most likely use some sort of screen reader or similar. You said your trying to add a freq to a list, presumably a favorites list the you or someone created. If you are somewhat familiar with Sentinel, then it's pretty much what I described in post 3, or here.
You can add a freq to a favorites list by reading the scanner into Sentinel, then edit the favorites list you want to add it, and then navigate to where you want it, and add it. The write back to the scanner.
If your not familiar with Sentinel, then see if you, or someone can get your favorites list exported from Sentinel, and zipped (compressed) and posted here in this thread with the freq you want added, and I am sure it can get done for you.