This is one of the easiest DIY maintenance things you can do your Subaru. I believe the dealership wanted to charge me $495 to do it. To DIY its about ~$40 in OEM coolant (from the dealership) and $30 in parts/tools. You could probably get by without the special funnel but it makes ‘bleeding’ the system more straightforward.
Like the CVT Fluid change, I did a lot of research and consolidated it into a list of steps then had ChatGPT organize it into a printable procedure PDF.