As @firenzel says. The install button is the small hole under the clip. Use a paperclip for one second after the Roger On is turned on and the number of licenses will show in the display. A couple of more seconds and the Roger On will enter the license transfer mode. As @kevels55 noted, the licenses can be replenished (apparently up to 5 times).
Don’t add another license coz if you read what @kevels55 said, it’ll load 2 licenses and over ride the other licence and so you’ll have 1 license less. Altho you may not need it.
When purchasing a second-hand Roger On In, determining if the two licenses are still available without having a hearing aid around can be tricky. One possible way to check is by contacting the seller and asking for the serial number of the Roger On In. With this information, you can reach out to the manufacturer or a local hearing aid specialist to verify the status of the licenses. They may be able to check the serial number against their database to see if the licenses are still available or have been transferred to other hearing aids.
If anyone has more insights or tips on how to verify the licenses of a second-hand Roger On In, I’d love to hear them!