Early 1990s NTSC video was generally mastered to different monitors than we have today. So you need to adjust gamma, saturation and hue. In fact the colorspace might even be slightly different, but I don’t think there’s any software to handle that.
So your best bet is to adjust “by hand”. You can use the TNG remasters are reference, since uniforms and some sets will be similar.
Or you can take a look here: http://blog.trekcore.com/2019/05/exclusive-star-trek-deep-space-nine-hd-what-we-left-behind-footage/On my tests I used something like gamma 1.4; saturation 130% and a -4% hue shift. Also clipped black a bit on levels.
Thanks for the tips, will see how I can apply them. Could you imagine what could be done with the original film? For DS9 it could perhaps be done in widescreen … Oh man, we can only dream.