Its construction is done in multiple stages.
First, you need to collect information on your current and future clients. You need to use a quantitative approach relative to sociodemographic criteria (gender, age, profession, socio-professional status, area of residence, etc.) as well as a qualitative approach relative to behavioural and psychological criteria (lifestyle, values, motivations, restraints, etc.).
Consider the information you already have at your disposal: your database, teams who are in direct contact with your clients, studies, etc. If you wish to procure more detailed data, consider sending out surveys. The objective is to collect information from your clients and your prospective clients by talking to them directly.