Should i use 1 cord fiber or Duplex Patch Cord between the media converters ? whats the different ?
It is likely that your 2nd question answers your 1st question, if you're asking about individual Tx and Rx connections into the converter or your router's optic, it's going to be duplex. Simplex (1 cord) fibers Transmit (Tx) and Receive (Rx) out of the same cord.
To add a bit more detail. If you're using single-mode fiber, then that means your router's optic (i.e. SFP) should be at least a "Long Range (LR)" optic. Whether it is simplex or duplex also depends upon what your router's SFP is expecting. Your router and media converter need to match in this way.
how to arrange cords to TX and/or to RX in both ends ??
Again, this implies a duplex cable. The way to arrange Tx and Rx is simple, arrange it so that the link comes up between the routers. This means you may have to disconnect the fiber, switch Tx and Rx on one side only and reconnect it so that the link comes up.