Under review since 9 months. Shall I send another email First, I would like to mention that I saw that there are similar questions about this topic on this site but this one is very specific whose answer I could not find anywhere. The query is as follows.

I had sent a manuscript to a springer electrical Journal, 10 months back. For 3 months, the status showed "With Editor". Then finally it changed to "Under Review". For the past seven months, it is "Under Review". One month back, I had sent a polite enquiry to a person in editorial office about my paper. He replied that he was sorry and he has contacted senior editor to speed up the process. Today, exactly one month has passed since his reply and the status still remains under review. The average time taken for the first decision as mentioned on the official journal website is 3.5 months. My fear is that the article has already taken nearly a year since I had send it and if there is any more delay, I would not be in a position to send it to any other journal because the proposed approach will become old by then. Shall I send another email to the editorial staff, given that I had already sent another email just a month before? What kind of email can be sent in such a situation ?
Yes. The person you contacted in the editorial office is paid to answer queries like yours. It's exactly why the publisher employs them! Feel free to email again, just don't be abusive (they do not directly handling your paper, and they cannot act without the editorial board's approval). I also suggest against threatening to withdraw your paper, because it's likely to be ineffective. At most the editorial office can only forward your message to the handling editor, and they're likely to say "okay, you can withdraw it" especially since they're evidently having trouble finding reviewers.

As for what to write in the email, it's up to you depending on what you want to know. You could ask them to chase the handling editor again. It's also possible they might be willing to tell you more details about the manuscript's status: how many reviewers have been invited, how many reviews have been completed (if any), when further reviews are expected (if there are reviewers who've agreed to review but have not submitted), and so on.