You need a business model that will attract both brands and influencers and still make money for you. You need to find a model which will be attractive for all parts. And that model must be competitive to your competitors in that market.
Next you should attract the influencers so they are willing to sell their services through your business.
Third you need to find way to sell to the brands. You could use a portal where brands can announce their deals, or you can give them the possibility to “browse the influencers”. Another way would be to be a subcontractor of a marketing company, and then let them sell for you. A third way could be to make exclusive contracts with a few companies. There are probably more ways.. use your fantasy.
You can find inspiration in existing influencer-portals. Just do a google search for “influencer marketing"
You are going into a highly competitive market, but it is also a growing market, so all the best to you.