If the problem is located in the Roku itself, a restart may fix it. If you have sufficient control via the remote you can restart via menu path starting at Roku home screen: Settings..System..System restart.
If you don't have sufficient remote control you can restart by unplugging from the power source then plugging back in after a few seconds.
If a restart doesn't fix it, the problem probably resides in the remote. All I can think of there is to remove the batteries for a few seconds then put them back in. If that doesn't get it, you probably will need to replace the remote.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T