I have a red and yellow complete set my 3rd move is rent them my opponent give a red/yellow wild property card. Now in this scenario what to do..? I have to leave it as it is or I have to create it as second set of red...?
You are free to reconfigure your card sets any way you like on your turn.
You can only reorganize your property collection on your turn.
You start a new set (since both of your red and yellow sets are already full), but you can start that with either the new red/yellow wild or one of the red or yellow cards from your existing sets (and put the wild card into that set to replace it).
You can move it to the properties' section, in this case you would have the two completed sets of red and yellow and a new one, red or yellow(you can choose the color).
With the thumb down I interpret that this is not what you wanted to know, I will assume that the information I gave you above you already knew it.
I think you want to know how to collect rent from those properties you described above, so this is my answer, in the card it says that you can collect rent from all properties of that color, so in this case if for example you choose the red color, you can collect rent from the red completed set, plus the red wild one.
If that is not what you want to know then I have no idea.