You should return to the marketplace to review your account information and select a new plan. In most states, if you do nothing, the marketplace will automatically renew you into a marketplace plan that is similar to what you had last year. However, depending on the marketplace plans available, you could end up in a plan that is in a different metal tier or is a different plan type than your old plan (for example, an HMO instead of a PPO). Your insurer should have sent you a notice if it is enrolling you into a similar plan.
If you are eligible for financial assistance through the marketplace, you should return to your account, review and update the information, and actively select a new plan. This will ensure that you receive an accurate amount of any premium tax credits and cost-sharing support you are entitled to and are enrolled in the best plan for your health care needs. (CMS, Guidance on Reenrollments and Redetermination for Exchange Coverage for 2018, July 13, 2017).