Ahsan, in many (most?) double trigger designs the triggers are not centered in the guard bow, but are offset to the right. This causes a left handed shooter to have to "reach through" the guard to get at the front trigger. The temptation is to simply unpin the triggers, swap positions and re-pin them. While this can (sometimes) be done it is generally unsatisfactory. The rear trigger will then be way off to the right and needs bending (not easy as annealing is required first). In addition the trigger blades are usually canted a little to accommodate a right handed shooter, and this "fix" does nothing to address that. Finally, it is tradition that the front trigger on a double gun shoots the more open choked barrel first and swapping the triggers reverses that situation. With choke tubes, you can reverse the tubes to suit, but that does not remedy the other issues outlined. The only real answer is to have proper left handed trigger blades installed, and in most cases these have to be custom made or modified. So, while the installation is mechanically simple the acquisition of suitable triggers is usually expensive. I should also mention that a right handed gun will also be cast off for a right handed shooter, so some stock bending will also be required (also not cheap).
Sharptail