When you miss first rakat of the prayer of Maghreb then how you paray your prayer?

If you miss the first rak'ah of Maghrib prayer, you should join the congregation during the second rak'ah. Once the prayer is completed, you should perform your missed rak'ah after the congregation finishes their prayer. This means you will stand up to complete your own prayer, making it a total of three rak'ahs (two with the congregation and one alone). Remember to recite the necessary verses and perform the final tashahhud before concluding your prayer.