Generally speaking, people choose according to their height and weight. If you don't know how to choose, you can refer to the following principles, according to the normal physique and exercise intensity of Chinese people, and consider the stage of increasing dumbbell fitness intensity in the future.
Height 1.60m, weight 60kg-25kg combination.
Height 1.70m, weight 70kg-30kg.
Height 1.80m, weight 80kg-35kg combination.
Height 1.90m, weight 95kg-45kg combination.
If the purpose of doing dumbbell exercise is to gain muscle, then do related dumbbell exercises in groups every day for 8RM- 10RM 5-6.
If the purpose of your dumbbell fitness is to keep fit, do some dumbbell exercises 15RM-20RM 5-6 groups every day.
I wish you early success. If it is useful to you, please choose a satisfactory answer, give an approval and encourage you.