If your NAMM membership has lapsed for more than 60 days, you can log into your company's NAMM Dashboard here: https://dashboard.namm.org/
Once logged in, you need to ensure your account has Admin or Billing access. Then you should see a Rejoin now button.
Selecting Rejoin now will bring you to a page to review your company's information, where you can make any edits if necessary.
You can then review benefits and pricing and submit your payment to reinstate your membership.