要在Android中使用RxJava3与Room结合，可以按照以下步骤进行操作：

1. 在build.gradle文件中添加依赖项：

dependencies {
    // Room
    implementation "androidx.room:room-runtime:2.3.0"
    annotationProcessor "androidx.room:room-compiler:2.3.0"

    // RxJava3
    implementation 'io.reactivex.rxjava3:rxjava:3.0.0'
    implementation 'io.reactivex.rxjava3:rxandroid:3.0.0'
}

2. 创建Room数据库：

@Database(entities = [User::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao

    companion object {
        @Volatile
        private var INSTANCE: AppDatabase? = null

        fun getInstance(context: Context): AppDatabase {
            return INSTANCE ?: synchronized(this) {
                val instance = Room.databaseBuilder(
                    context.applicationContext,
                    AppDatabase::class.java,
                    "app_database"
                ).build()
                INSTANCE = instance
                instance
            }
        }
    }
}

3. 创建实体类：

@Entity(tableName = "users")
data class User(
    @PrimaryKey val id: Int,
    val name: String,
    val email: String
)

4. 创建DAO接口：

@Dao
interface UserDao {
    @Query("SELECT * FROM users")
    fun getUsers(): Flowable>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertUser(user: User)
}

5. 使用RxJava3进行数据访问：

class UserRepository(private val userDao: UserDao) {
    fun getUsers(): Flowable> {
        return userDao.getUsers()
    }

    fun insertUser(user: User) {
        userDao.insertUser(user)
    }
}

6. 在Activity或Fragment中使用Repository获取数据：

class MainActivity : AppCompatActivity() {
    private lateinit var userRepository: UserRepository

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val userDao = AppDatabase.getInstance(this).userDao()
        userRepository = UserRepository(userDao)

        userRepository.getUsers()
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe { users ->
                // 处理获取到的用户数据
            }

        val user = User(1, "John Doe", "johndoe@example.com")
        userRepository.insertUser(user)
    }
}

通过以上步骤，您可以将RxJava3与Android Room结合使用，并在Android应用中进行数据访问和处理。