I did not apply for this seminar, but forwarded it to Irene to see whether she is interest or not
This is an informal communication, so you could use a contraction (which is easier on the English ear - Americans seldom seem to use them.)
This is colloquial speech:
I didn't apply for this seminar (myself), but I sent it on to Irene to see if she was interested or not.
This is formal speech:
I did not apply for this seminar (myself), but I did forward it to Irene to see whether she is/was interested.
'is/was' depends on whether the seminar has been held or not.