Updating iTunes on iMac- updating process locked itself

I have an iMac (2011) operating on High Sierra. When I tried to backup my new iPhone it asked for updating iTunes. I started updating, but then my internet connection failed. When my Internett was back again, the updating process stopped and i got the message "Cannot open iTunes because it is updating". Since the message has been sent for over to days, I presume the updating has stopped and locks my i Tunes.

Any ideas how to deal with this problem?