That means it is Roku tv remote, which uses different IR commands then roku streamer like the express. What is the model number of the remote, its in the battery compartment? Is there a pairing button there?
I hoping if there was pairing button, it could have been paired to the 3900, but witout one its just useless to you roku tv remote. Just make sure the next remote doesn't have tv controls, which are only roku tv use. Like the last remote priced at $14.99 on this page:
Or go with a non-roku remote like this universal remote, works with roku boxes, roku TV's, and many other brands of streamer, I like it a lot myself:
Will control your tv or sound bar too, and is a learning remote.
Works for me, the first link has four remotes listed above one another, you don't what the first three, its the fourth priced at $14.99 listed as Standard IR roku remote.
The second link is to one open box One-For-All urc-7935 Streamer remote, usually going for $24.99, here its $9.99