Tip 1: Understand your responsibility
As a product owner, you are responsible to ensure you and your team are aware and comply with your organisation's accessibility requirements. If your organisation doesn't have such requirements, you should consider defining what you believe to be the minimum requirements - being mindful that developing an app that is accessible and inclusive, will be usable and benefit a wider range of user groups.
Setting such requirements requires buy-in from the team, and you should research accessibility guidelines and clearly communicate your expectations with your delivery team.
Below are links to some resources that may help you understand general accessibility guidleines together with how some organisaitons have defined their requirements:
Tip 2: Capture diverse personas
When we think of users of our products, we can sometimes forget to include a diverse set of users and use cases. Consider how someone with auditory, cognitive, physical, speech and visual disabilities might go about using your app. What if your users included the elderly with age-related impairments. What if someone was to use your product while having a situational limitation (e.g. outside, on a sunny but glary day) or with temporary impairment (a broken index finger or a finger with a bandaid).
The above are just examples of real-life users that may be using your product and you should consider them when planning out features and functioanlity.
Although it refers to web users, the W3C Diversity of Web Users is a handy resource to refer to and help build awareness with your team.
Tip 3: Include accessibility acceptance criteria
No matter if you follow a waterfall or agile software delivery model, your software needs to go through formal acceptance before it is considered done and complete. Ensure the features you and your team define also include accessibility acceptance criteria. This will ensure that your designers, developers and testers consider and deliver those features with the acceptance criteria front of mind.