The idea of nirvana rather than being approached from through the four noble truths can be approached through the three dhamma seals, but before we go there, I want to try to define what Nirvana is:
First, a quote from the Rissho Kosei Kai, a lay mahayana buddhist organization in the nichiren tradition who also rely on the buddha's early teachings:
The key point that I take away from this is that Nirvana is a state of peace. This peace never leaves you, meaning you have perfect freedom, meaning you have a kind of relaxed fortitude - It acts as a ship, floating on the sea of suffering while others may be drowing in it.We undergo various sufferings in life because we are swayed by changing phenomena and are influenced by immediate gain or loss. If we come to have the spirit of perfect freedom, being detached from these temporary and superficial considerations, we will be in a spiritual condition of peace and calm even when we are in a situation that others consider to be very painful. This is the state of "Nirvana is quiescence"...(1)
Some people would say that nirvana is "bliss" but this bliss is simply a result of the state of freedom.
So how do you go about finding this peace? For a temporary peace or provisional 'taste' of nirvana, I believe that you simply need to practice samatha meditation, but if like the buddha, you wish for permanent peace then you need to uproot the deep seated delusion embedded deeply into your life. You must overcome the three "poisons" of Greed, Anger and Ignorance. Of the three, Greed and Anger are the most easy to subdue as they can be identified easily, while Ignorance is much more difficult to subdue as it appears in myriad different forms.
This is where the three dhamma seals come in: Impermenance, Emptiness and Suffering/Nirvana; removing the sources of delusion.
Impermenance helps us see that everything in this life is transient and therefore not a solid base on which to build peace and happiness.
Emptiness teaches us that a large source of ignorance is caused by the small ego.
The common link between impermenance and emptiness is that we are clinging to things with no real foundation, and therefore, ultimately cause more suffering when our castle comes crumbling down.
If you explore the three dhamma seals to reveal their all their implications and then base your behaviour and thoughts on them then you can uproot all sources of ignorance and actualize true wisdom. It is said that any true teaching of the buddha is derived from the three dhamma seals - this includes the aforementioned four noble truths and the eightfold path. So a deep understanding of the three dhamma seals will reveal to you a "birds eye view" of the buddha's teachings, a philosophical base of concepts from which the more practical 4nt and 8fp are derived.
When you succeed in reaching nirvana - however long it takes you - then you will reach a state of unchanging peace
(1)https://rk-world.org/3seals.aspx