This is general-purpose article. You can use a more specific articles

How to send alerts from Discord to MetaTrader 4/5

How to send alerts from MetaTrader 4/5 to Discord

How to send alerts from Telegram to MetaTrader 4/5

How to send alerts from MetaTrader 4/5 to Telegram

How to send alerts from TradingView to MetaTrader 4/5

1. Download AdvancedNotificationsLib.dll into MQL4/Libraries or MQL5/Libraries folder.
2. Modify your strategy code:

• Import AdvancedNotificationsLib.dll

  #import "AdvancedNotificationsLib.dll"
  void AdvancedAlert(string key, string text, string instrument, string timeframe);
  #import
  

• Send the telegram message by calling AdvancedAlert

  AdvancedAlert(AlertKey, message, Symbol, "m1");
  

You can find a real-world example here: MT4 Engulfing Pattern with Telegram alerts