As per the error message looks like your function is unable to find the azure storage assembly. Can you refer to this document and install the storage extension.
To access the blob inside within the event grid trigger you need to use storage SDK and write your own code to read the blob. Once you are done with the operation you can define the storage output binding that allows you to modify/delete the blob storage data. Make sure to review the Usage that will help you with supported bind types to write blobs.
string connectionString = "yourconnectionstring";
CloudStorageAccount storageAccount = CloudStorageAccount.Parse(connectionString);
blob = new CloudBlockBlob(new Uri(eventData.Url),storageAccount.Credentials);