If you do not have an active subscription, you can still log into your account and join your gym. Head to www.btwb.com and log in using your current email and password, from here you will be prompted to purchase a new subscription. However, you can bypass this page by selecting "Switch gyms".
From here, you will be taken to your profile setting, select "Change gym association".
Enter your gym name and member code. Your coaches will have given you your gym's specific code to join. If you don't know your gym's Member Code, just hit the "Send Request" option instead. A coach/admin for the gym will be able to approve/deny your request.
Select "Submit" and you will be able to continue using CrossFit BTWB with all your data still saved to your account.