There are two ways of counting how far advanced your pregnancy is: gestational age and fetal or embryonic age. Flo shows gestational age, calculated from the first day of your last period. Gestational age usually differs from the fetal age by 2 weeks.
Although the week of pregnancy can be changed (tap Menu > Pregnancy settings > Gestational age), we do not recommend you change it. All insights you receive are based on the gestational age. So if you change it, the articles may no longer be relevant to you.