There are many web content writers. If you are an editor or copyeditor, you can start a company offering to edit web content. You can work as an online editor, in which web content writers can send you their web content via email, you edit it and return it via email.
You can advertise on many of the freelance writer websites.
If web content writers include their email addresses, then you can also contact them about web content editing.
This includes spelling, grammar, sentence structure. You can edit for content itself. Suggest more interesting titles to attract readers, including uses of keywords. You can also offer to do fact checking and research.
You should set up a website.
To find customers, you can also write articles on web content writing and web content subjects, including a link to your website. These articles along with your first few clients can help to establish you as an expert in the areas of web content editing and copyediting.
You can also list as a web content editor at writers.net.
Of course, editors and copyeditors don't have to be writers themselves. There are many editors and copyeditors in publishing who are not necessarily the best writers themselves, but they are the best editors and copyeditors and writers rely upon these editors and copyeditors to help these to produce the most excellent manuscripts.
It's possible also to work as an acquisitions editor of web content, in which your company acquires web content, edits it and then submits it to web content markets.
Because web content is so easy to get online, many writers put web content online without always checking adequately for spelling and grammar and content and facts. Often these writers, because of the nature of the internet, do their own spelling, grammar, content, and fact checking.
You must also decide what are your fees, per page or per word. If you do research, how much do you charge for research? Fact checking? Your fees can be custom fees per client and/or set fees.
You can work with clients as a freelance editor, copyeditor, acquisitions editor.