Can’t download apps previously downloaded

Unfortunately you have provided too little information for us to propose a specific solution. Describing what happens when you try, and the exact wording of any error messages, would greatly aid us in helping you. In the meantime review these suggestions and documents if you think they apply:

Read this document if you can’t download or update apps on your iPhone or iPad --> If you can’t download or update apps on your iPhone or iPad - Apple Support

If the first 5 don't help, use the 6th.