رَبِّ ٱشْرَحْ لِى صَدْرِى وَيَسِّرْ لِىٓ أَمْرِى وَٱحْلُلْ عُقْدَةً مِّن لِّسَانِى يَفْقَهُوا۟ قَوْلِى
Rabbish rah lii sadrii wa yassir liii amrii wahlul 'uqdatam milli saanii yafqahuu qawlii
My Lord, expand for me my breast (with assurance) ease for me my task and untie the knot from my tongue that they may understand my speech.
This dua originated when Prophet Musa AS was given the important task of spreading His teachings. In one of his mission, he is expected to see Firaun and warned him that he has overstepped the boundaries and that if he does not ask for Allah's forgiveness, then he would be punished. This was not an easy task, especially knowing Firaun's history of tyranny and the practices of his people. So in order to be able to get through these hardships, he recited this dua to Allah in order to ask for strength and have the courage to go through this challenge.
This dua is recited to ask Allah to make his mission easy, clear his chest, and let the knot of his tongue be loosened in order to deliver His message and therefore have the people understand the message of Allah. Hopefully, the same will also apply to us by reciting this dua. Whenever there are hardships and are required to speak up or be courageous, then InshAllah we will gain His blessings and make the issues that lie ahead of you to be easier.