Take a small flat blade screwdriver and put it down in the joiner where the rail would fit.
And twist it, to open up the joiner, yes this will destroy said joiner.
Once you have opened it up wide, it is possible to gently work the joiner from the rail with a back and forth motion (side to side) with needle nose pliers.
Be careful not to pull the rail from the "spikes" on the ties.
If you're running on 11.25r or better, short shank couplers will work in most cases.
If the wheelsets roll very freely in their trucks a coupler swap maybe all that is necessary.
If they don't, consider changing the trucks with the couplers (as one unit) as well, as Len suggests.
Good luck
And twist it, to open up the joiner, yes this will destroy said joiner.
Once you have opened it up wide, it is possible to gently work the joiner from the rail with a back and forth motion (side to side) with needle nose pliers.
Be careful not to pull the rail from the "spikes" on the ties.
If you're running on 11.25r or better, short shank couplers will work in most cases.
If the wheelsets roll very freely in their trucks a coupler swap maybe all that is necessary.
If they don't, consider changing the trucks with the couplers (as one unit) as well, as Len suggests.
Good luck