I have been playing the reti with 1NF3 2C4 for the past 1 month and want to find a dynamic response to the advance variation (...2 d4) as the engine considers it to be the most critical try for black
A good try for a dynamic game is 3.e3, against which Black has two main replies: 3...c5 and 3...Nc6. Against 3...c5 you could opt for either 4.exd4 or 4.b4, being a tempo up in the Modern Benoni or Blumenfeld gambit respectively. Both of these openings are known to be quite dynamic, so if you're ahead an extra tempo it can only help you.
In the case of 3...Nc6, the main line goes 4.exd4 Nxd4 5.Nxd4 Qxd4. The position is around equal - White is a bit cramped and the d-pawn could end up being backward, but Black will have to spend a bit of time moving the queen around. If this isn't to your taste, then after 3...Nc6 you could instead go for 4.b4!? dxe3 5.fxe3 Nxb4 6.Nc3, with some compensation for the sacrificed pawn. Further study will be required here to understand how to best develop and make use of your compensation for attacking.
On the third move instead of 3.e3, you could also consider 3.b4. White enables the bishop to go to b2 and attack the d4-pawn. The b4-pawn also puts itself in a position where it could attack Black's knight arriving on c6, while at the same time monitoring the c5-square. However, I don't think 3.b4 is quite as dynamic as 3.e3, as you're not immediately putting pressure on the d4-pawn -- this gives Black the freedom to choose from a number of continuations, such as 3...f6 4.e3 e5. So while 3.b4 is definitely not any worse from an objective standpoint, for the sake of learning less theory while also getting a dynamic game, I'd recommend 3.e3.