Hi Chinna,
I don't know how clearly I understood your requirement, but based on what I understood, you can try this once and see if it works -
For the target element of tag2:
Use ifWithoutElse where if condition will be on tag3 (tag3 EXISTS)
if this holds true, then pass tag2 forward to the target element.
If this doesn't work out, it would be easy to have a look at the source/target structure, please provide if possible.
Regards,
Abhishek