import { Marker } from 'react-native-maps';
import { ClusterMap } from 'react-native-cluster-map';

<ClusterMap
  region={{
    latitude: 37.78825,
    longitude: -122.4324,
    latitudeDelta: 0.0922,
    longitudeDelta: 0.0421,
  }}
>
  <Marker coordinate={{ latitude: 37.78725, longitude: -122.434 }} />
  <Marker coordinate={{ latitude: 37.789, longitude: -122.431 }} />
  <Marker coordinate={{ latitude: 37.78825, longitude: -122.4324 }} />
</ClusterMap>;

import { Marker } from "react-native-maps";
import { MyCluster } from "./MyCluster";

// ...

renderCustomClusterMarker = (count) => <MyCluster count={count} />

render () {
  const { markers, region } = this.state;
  return (
    <ClusterMap
      renderClusterMarker={this.renderCustomClusterMarker}
      region={region}
    >
      {markers.map((marker) => (
          <Marker {...marker} />
      ))}
    <ClusterMap>
  )
}

import * as React from 'react';
import { View, Text, StyleSheet } from 'react-native';

export const MyCluster = (props) => {
  const { count } = props;
  return (
    <View style={styles}>
      <Text>{count}</Text>
    </View>
  );
};

const styles = StyleSheet.create({
  width: 50,
  height: 50,
  borderRadius: 25,
  backgroundColor: 'red',
  justifyContent: 'center',
  alignItems: 'center',
});