In the Kpop industry, groups debut in primarily two ways- the first is as a part of entertainment labels where the group is formed by the company from its own pool of trainees. All decisions regarding the formation of the group are made solely by the company. Examples, BTS, Seventeen, etc
The second way groups are formed is through survival shows- where contestants come independently or from different companies, and must place within a particular rank to debut. The final debuting group is decided purely on the basis of public voting. Eg, in Boys Planet, the top 9 placed individuals have formed a group.