Seemingly, architecture and Agile development methodologies are in an adversarial relationship, and there are many myths around this topic. There are a few simple principles that you should follow in order to develop your product in an Agile way while still caring about its architecture.
Agile, by nature, is iterative and incremental. This means preparing a big, upfront design is not an option in an Agile approach to architecture. Instead, a small, but still reasonable upfront design should be proposed. It's best if it comes with a log of decisions with the rationale for each of them. This way, if the product vision changes, the architecture can evolve with it. To support frequent release delivery, the upfront design should then be updated incrementally. Architecture developed this way is called evolutionary architecture.
Managing architecture doesn't need to mean keeping massive documentation. In fact, documentation should cover only what's essential as this way it's easier to keep it up to date. It should be simple and cover only the relevant views of the system.
There's also the myth of the architect as the single source of truth and the ultimate decision-maker. In Agile environments, it's the teams who are making decisions. Having said that, it's crucial that the stakeholders are contributing to the decision-making process – after all, their points of view shape how the solution should look.
An architect should remain part of the development team as often they're bringing strong technical expertise and years of experience to the table. They should also take part in making estimations and plan the architecture changes needed before each iteration.
In order for your team to remain Agile, you should think of ways to work efficiently and only on what's important. A good idea to embrace to achieve those goals is domain-driven design.