Welcome to Jimkim

There is no way to merge accounts with different airlines, except in rare instances when one airline buys another and amalgamates the 2 frequent flyer programs (eg Delta & Northwest, Lufthansa & Swiss).

Here is what I would do. Pick one of the programs to be your main one going forward.

For the other program, if very small number of miles abandon them, if modest amount then either redeem as is or credit a little more to top up for an worthwhile and easily attainable award, if lots of miles then have a plan to run off the mileage balance.