If you want to do so then you can't take admission directly to the 12th in UP Board. You have to cancel your admission in CBSE and then you have register in the UP Board as a student from the 11th and this way obviously you can do so.

To know more about UP Board class 12th visit the link below:

https://school.careers360.com/exams/up-board-12th

To know more about CBSE 12th visit the link below:

https://school.careers360.com/exams/cbse-class-12th

I hope this answer helps. All the very best for your future endeavors!