To join the loyalty programme, simply create a customer account on lescollectionneurs.com. From there, you can choose to upgrade to Premium membership.
If you were already a loyalty programme member before April 2022, you should have received an automatic email asking you to reset your password and thereby migrate your existing account to the new customer account area.
If you did not receive this email, go to "Login" and click on "Forgot your password?". You will then receive a new password reset email.