How to assign a project to a sale order once both are already created


I have created a quotation and then I have created a sale order from it.

On the other hand, I have created a project before with only one task so far.

I need to assign that project to the quotation. At the moment, I have only found a way to create a new project from the sale order or a new sale order from a project. But, what if both already exists? I need to attach the project to the sale order. Is it possible?