I have 3 ROKU devices. I can access 2, but can't access the 3rd one. Evidently when I first set up my ROKU account "years ago", they need my password. I told them I dont know it. Now they tell me that the name on the account that I can't access, does not match all the names of my family that might be on the original account. I must have gotten at least 6 emails asking for the same info. I send what I know and get the same questions. No phone call even though they wanted me to verify my tel. number. I wish there was another option to ROKU. I would change in a heartbeat. Very frustrating.
It's not clear what your problem is. Do you have 2 different Roku accounts? Do you want 2 different accounts? Why don't you just factory reset your 3rd Roku and link it to the account of the 2 working Rokus?