Anything that might bias your data or interpretations of your research must be fully disclosed when you submit your manuscript. Hence, most journals will require a Conflict of Interest statement in your manuscript or cover letter.
Conflicts of Interest is the section where you should mention:
If a company has funded your research, you may need to explain the role the company has played in the analysis and interpretation of your data.
You might have a co-author who has a conflict of interest. It is helpful to know this before you design your research so you can try to avoid possible bias. For example, you might try blinding that author during the data analysis stage.
Some journals require you to submit a Conflict of Interest declaration form along with your manuscript. Read the journal’s author guidelines carefully to see if this declaration is needed.