There are very few companies that will invest in a product that has not gone through a professional based patenting process. They are likely not to want to license a product like this, not to partner with inventors who use these methods or provide any development of such products. There are risks involved in this situation for them and they will not give you money for your invention unless a patent attorney has gone through the process with you.
The fact is, if you have an improvement to a product that is significant and considered unique enough, then you have the right to that patent. In fact, even if another company is marketing the existing product, your idea or invention cannot be in use by or marketed by them unless they have your permission to do so as you can read from https://www.techtimes.com/articles/249715/20200518/how-inventhelp-gets-new-inventors-onto-the-right-path.htm.
When can you use such a situation? For example, if you have an idea to improve product XYZ from ABC Company and they have the full license to the existing product and they are marketing it, your invention that in some way improves their product can be permissible. This is one of the best ways to get into a large invention contract even multibillion dollar companies cannot work against you if you have put in place a patent on your improvement to their product.
Of course, for this process to work, your patent must be valid and it should always be done by a professional, experienced patent attorney or patent agency as described on https://www.valuewalk.com/2020/05/medical-invention-covid-19/. In doing so, you insure that your patent is legally binding which helps to protect you from the company filing claims against you. The process can be lengthy, as any patent process is. But, a provisional patent can give you that patent pending protection that you need until you have ironed out the details and have your patent in hand. In many cases, this process is the fastest and safest way to protect your idea.