In Duas Yastasheer , I always read that Allah(swt) Is the succorer of those who have a pure heart. So I often ask this in my duas
But what does that really mean?
Is it the fact to dont have animosity ?

May I know some things to do to have pure heart? Or things to increase noor in our heart?

Yes it’s true and Quran mentions this clearly that the guidance is with Allah. even one of the best names amongst Asma ul Husna is Al-Hadi.
But what should we do to get His holy Guidance ?
We must rely on Allah in all our affairs we must leave all our wishes and submit to Allah then most surely He will not leave us to go on astray.
Also we must follow His command without any question that we call true obedience if we become true Servant of Allah He will give us power that none can have.

وَمَن يَهْدِ اللَّهُ فَمَا لَهُ مِن مُّضِلٍّ أَلَيْسَ اللَّهُ
بِعَزِيزٍ ذِي انتِقَامٍ

And whom Allah guides, there is none that can lead him astray; is not Allah Mighty, the Lord of retribution?(39:37)

‎إِنَّكَ لَا تَهْدِي مَنْ أَحْبَبْتَ وَلَٰكِنَّ اللَّهَ يَهْدِي مَن يَشَاءُ وَهُوَ أَعْلَمُ بِالْمُهْتَدِينَ

Surely you cannot guide whom you love, but Allah guides whom He pleases, and He knows best the followers of the right way.(28:56)