Is conflict of interest applicable for independent research?
If your case is a case in which conflicts of interest do not apply, then you simply state:


  The author declares that she/he has no conflict of interest


assuming you are the sole author, in the appropriate section, usually stated Conflict of Interests. Note that some publishers, such as Elsevier, require you to sign a form for this purpose as well before even beginning the review process.

For further information you may refer this post:

Clear explanation of Conflict of Interest with examples in journal articles