If you happen to know the Account ID of the user you want to follow, you just have to plug in the right number where I’ve written (User Account ID) and you should be good to go. See a completed example below. If you don’t know the ID you’re after, read the following steps.
To find Twitter account IDs, the easiest method is to use ID from User. Type in the user name of the account that you’re interested in following, and this cool little tool will automatically generate the Twitter account ID you need.
Again, finish off by inserting the ID that you just found into the Twitter RSS URL and you’re all set