u need editing software (coreldraw, photoshop etc) and a plugin KK_AccessoryClothes.dll
1. export the "UV maps" and maintex of both cloth part
2. using that UV maps as template u can make new AlphaMask png (black = invisible and white = visible) or erase the part from maintex if alphamask method doesnt work (for this case remove the skirt area from set 1 and remove the torso area from set 2)
3. put the 1 part on the clothes slot while the other on acc slot
KK_AccessoryClothes.dll plugin allow u to use 4 top (1 on cloth tab and 3 on acc slot).
note that 90% of the time it wont mesh well since modder usually use different 3d model so the fit wont be 100% match.
using different part still work tho for example top from makise, glove from lor and shoe from edge etc.
another way by brute force method, it would be similar to above but u just need to mess with 1 version and on this case the 2nd set.
just erase the chest area from maintex but it will always be on that state since the texture are missing even at fully clothed.