Dry Rot (?) in Exterior Trim, patch or replace?
Don’t fiddle with epoxy. You’ll want to remove those boards and see what’s happening on the other side. You’ll want to replace the boards. As mentioned in the comments - you’ll need to assess why the wood rotted. First place to look is the flashing/trim right above the rotten boards - is water getting behind it and the rotten boards? Around it? Next time it rains go have a look at the situation - is water dripping off the edge of the flashing/trim to the ground, or is it working around the flashing/trim and running down the face of the rotten boards? Water is somehow collecting somewhere it’s not supposed to be.