Perform a Factory reset to wipe out all settings from its memory. It will restart snd you'll have to set it up from scratch as though it were a new set, this time linking to your desired account.
I'm not where I can check but from memory the menu path is Settings - System - Advanced system settings - Factory reset
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking " as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X