You can, actually, take all the essential steps on your own (build everything from scratch). However, this will require a lot of effort. You will need to build an acquiring relationship, form a risk department, ensure respective financial guarrantees, formulate legal documents. There are consulting companies that could help you with all these steps, but this is a longer way to becoming a payment facilitator.
On the other hand, there are companies that already have most of the essentials in place. They can either integrate you as a platform (if you are a platform), or, otherwise, sponsor you as a PayFac. One of such companies is ZiftPay.
Beside that, you can address the payment processor directly and ask if it has a payment facilitator program. Again, if you do not have experience and do not turn to consultants, the process will, probably, take time.
If you are developing a software platform and want to follow PayFac model, then rather thatn building the structure yourself, you could partner with some company like Zift. This option should save you resources and efforts.