How can I repair this wood window trim?
I see damage to sill (under window), brick mold (covers/protects L/R window edge).  Not shown but certainly contributing is the flashing/dripedge/overhang ABOVE window.  

If rot extends through sill and there wasn't proper waterproofing UNDER the sill and above the basic framing, your wall below the window is at risk.

This looks like a replacement window job that didn't address water-shedding/building integration.

As such, a replacement window is relatively easily removed.  Replacement wood and the rot issues can dealt with much easier.  Then waterproofing can be integrated below, on sides and above.

This JLC article deals with replacement windows in brick, flashing and water management.