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 "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X