I haven't watch the Kiss series. Will I still be able to understand the plot?
Yes you won't really be introduced to all the side characters in the same way as if you watch the other seasons but you should be able to get the drift of how the couples got together and have reached this point.
my question is, why they make another drama with the same story, same title and from same country with a year…
If i remember correctly two studios bought the right to the original book at the same time. The one that came out 2019 is shorter and they got it out first while Hu Yi Tian was filming go go squid and its longer soi assume to avoid conflict with the first version will be coming out 2020