If you are familiar with how to write patent documents, you don't need to find an agency. If you don't know how to write it, it is recommended to find a professional agency. Because the writing of the patent claim is very important and the description is too detailed, the protection scope of the patent claim is small, and there is also a relationship between the specification and the claim, which is also very important.
If you apply by yourself, you need to write claims, instructions, background technology, drawings and examples, if any.