Procedures for renewing a CNA license (expired or otherwise) depends on the procedures of the individual state's nurse aide registry; each state may have different procedures and only processes for its own state. (as in, West Virginia's procedures for renewal only applies to West Virginia registrations; West Virginia cannot renew any other state registration, and other state's processes cannot be applied to West Virginia renewals)
A little advice I can offer on finding nurse aide registry websites, applications, contact info, etc. is to look for the websites that end in .org or .gov as those are usually connected to state or local government resources, maybe something along the lines of (state) nurse aide program, nurse aide registry, board of nursing, etc. Again, the title/office/entity may vary between states, but ultimately focus on whatever entity is responsible for the state's nurse aide business. When you find the necessary information, you might even try to save it, bookmark it, keep notes, or some kind of reference to help you easily find it when needed again.
Acquainting with the processes and criteria for renewal wherever you are certified would be a very good idea. Some states may require an application to be submitted, offer a fee, or need additional documents, or classes/training to be attended. Maybe certain work experience can't be accepted. A certain amount of hours may need to be worked or a nurse aide may need to be currently employed. Maybe a combination of these things need to be done within a certain timeframe before or after expiration. What you need to do may depend on how long your license is expired. Maybe superiors complete or assist with the process or maybe it's the nurse aide's responsibility. A few states may not even have expirations or renewals, or leniencies may be in place due to the pandemic. (I would not know specifically which states do what though)
Also know that just sending or submitting stuff doesn't automatically change your status. It may need to be reviewed or processed and is possibly one of dozens the office receives at a given time.
Maybe the wrong form was sent or it needs to be sent a certain way ( i.e. WV recommends submitting via computer, not a cell phone). Maybe perchance the wrong form was done--which can be the case sometimes if completing an application not associated with the nurse aide registry. Or maybe sending something isn't part of the renewal process (which makes knowing about the proper procedure for the state important).
Because renewals can take some time as well, plan on managing it as early as you can to avoid or alleviate potential issues. One example of that I can give is that work or employment may be on the line after licenses expire (At least in WV, working CNAs with expired licenses is up to the individual facilities. In which case employer's policies regarding work with an expired license may be something else to familiarize with)
In short, learn what you need to do for renewals in your state, do your part as soon as you can, and try to be flexible and patient as the process takes place. Like with transfers/reciprocities, the registry may have their own way of informing your renewed status you might want to watch out for too.