You've already disassociated the client account from the technician account by unlinking them, however if the login Username/Email is the same in both accounts it'll prioritise the technician.
You should rename the tech account login and email details to something else so it doesn't go for the technician when logging in; not including first and last name so History is retained appropriately.
On the other hand, you could delete the technician account as they're no longer needed, however this will remove the corresponding link to tickets and details. - I don't recommend this, and I think it's best practice not to do this.
Thank you! Renaming the tech login fixed it.