Please note that connection-related issues cannot be resolved individually as the server operates the same for all players.
1. Go to Settings.
2. Tap on Wi-Fi or Data (depending on your connection type).
3. Turn the Wi-Fi or Data off.
4. Wait a few seconds.
5. Turn the Wi-Fi or Data back on / switch between your connection types.
As for additionals recommendations:
Shut down all background applications to reduce your processor and RAM load;
If you are using a VPN or proxy server, try disabling it as it may slow down your connection;
In case the issue persists, please reinstall the game.