A family of Microsoft relational database management systems designed for ease of use.
The problem here is we don't know the structure of your database. Do you store the date that registration was last renewed or the date that it expires. That is a key piece of information.
What you need is two fold. First you need a query that returns all pieces of equipment that need to be registered in the next 30 days. So you need criteria that will return those records. You can use the DateAdd function and return all records where the current date is greater than 30 days prior to the registration date. But without knowing how you know the registration date, we can't give you the correct expression.
The second part is running this query. I would create a report based on the query and run it as needed. However, if you want to run it automatically, that's a different story.