You can input your measurements while processing your first order, right after the Cart Page.
First, you will be asked to input your height, weight, age and body constitution. Then you will be able to input your measurements. It’s quite likely that the system can estimate your measurements and they are already there without you needing to get actually measured. You can learn more about it here: Why are my measurements already estimated?
Measurements in my User Area
Once you have placed an order you can always check your measurements profiles In your Customer Area. In your personal account, just click on “Profiles” and you will be able to create a new measurements profile or modify an existing one Customer Measurement Profiles.
In case you want to check what profile has been used in a specific order, you need to check it in this other section: Order History