How to convert interface to another interface which it implements?

In short - I would like to be able to cast an interface type whose underlying type implements a specific interface to that specific interface.

I am using the plugin package to lookup a New function which looks like so (I have many others the same):

func NewDomainPrimaryKey() any { return DomainPrimaryKey{} }

(This is generated at run-time so I can't just reference it as DomainPrimaryKey)

My lookup and call is like so:

                plugin, err := plugin.Open("my-plugin")
                if err != nil {
                    return err
                }

                symGet, err := plugin.Lookup("New" + pluginName)
                if err != nil {
                    return err
                }

                newGenModel, ok := symGet.(func() any)
                if !ok {
                    return errors.New("unexpected type from module symbol")
                }

                anyGenModel := newGenModel()
                genModel, ok := anyGenModel.(GenModel) // **this is where the problem is
                if !ok {
                    return errors.New("unexpected type from module symbol")
                }

                genModelInstance := genModel.Get()

In the above I am trying to cast 'anyGenModel' (an interface) to the 'GenModel' interface which it implements, however, this doesn't work.

I am certain it implements this interface because when I do the following, I get no errors.

type GenModel interface {
    Get() any
    TableName() string
}

var _ GenModel = (*DomainPrimaryKey)(nil) // this doesn't complain

How can I do this? I found this article which I don't think is what I am looking for but seems similar.

Thanks in advance for any help on this - this has become a real blocker for me.