agile solution architect

There are only three roles in Scrum, the Developers, the PO and the SM! 

As per the Scrum Guide: 

The Scrum Team consists of one Scrum Master, one Product Owner, and Developers. Within a Scrum Team, there are no sub-teams or hierarchies. It is a cohesive unit of professionals focused on one objective at a time, the Product Goal.

Scrum Teams are cross-functional, meaning the members have all the skills necessary to create value each Sprint. They are also self-managing, meaning they internally decide who does what, when, and how.

The Scrum Team is responsible for all product-related activities from stakeholder collaboration, verification, maintenance, operation, experimentation, research and development, and anything else that might be required.

The specific skills needed by the Developers are often broad and will vary with the domain of work.

I need to know what is the optimal way to apply the role of solution architects in Scrum

Why? Where does this so-called "role" come from? I'd suggest that there is no optimal way of succumbing to organizational gravity.

Instead, perhaps you should explain that this confection presents a constraint, that the challenge is more one of solution architecture, and that the Developers are held jointly accountable for any decisions made about how to build a quality product.

Thanks for replies

I think the word ROLE made some confusion

In fact, I didn't mean a role in scrum; instead, I meant a (Role in Development team, like developer, SA, BA, ... etc)

I read some articles that explain how does Agile deal with the JOB of architects in Agile (Or scrum) by giving different ideas!

Some suggest that the architect should be ONE person the has ONLY ONE JOB in development team as an architect!, and other suggest that each developer can act as architect

What I understood from  Ian Mitchell reply is that he suggest to let the development team to decide how to apply the architect JOB; and I think that this is the best way

if I didn't get the idea of Ian Mitchell, please tell me

Thanks

Mostly solution architecture are not agile as far as I have seen it is done in the same way as in traditional model. There will be dedicated Architects(external consultants) who give solution walkthroughs to relevant stakeholders and once it is finalised, the development will start in sprints. This happens in large programs to build a product. During development sprints, I have seen them helping PO to understand the flow and participate in backlog item creation. 

When dedicated person doing this job, the work is not distributed among all in the team. Because during sprints they may not involve in coding or testing. So my perspective is to have the team accountable for the solution decision as Ian mentioned. But at the start it may bring some challenges to the team to operate this way and many developers may hesitate if they have experience egos.