as far as I know that’s only possible if your ticket is full-fare Y fare-class. However, someone needs to confirm this as my knowledge is not reliable on this.

Edit: It seems like you need to buy a Y or B fare-class ticket to be able to upgrade your TK-operated flight with UA miles. Y or B fare-class tickets are likely to be more expensive than a discount business class ticket.

https://www.united.com/ual/en/us/fly/mileageplus/awards/upgrade/star-alliance-upgrade-awards.html