If you are alloted the seat in the first round but If you wish to join and proceed for upgradation, then you will retain the seat incase you are not allotted any seat in round two and  If you wish to leave the seat then, you will have 48 hours to do so. You can check the further information with the given below link.

https://medicine.careers360.com/articles/uttarakhand-mbbs-counselling

Good Luck!