Sounds like you need to focus on your interpersonal skills AKA soft skills. This book helped me connect with customers more. You'll have to work on your confidence but that's all about being sure of yourself but this should help. It's been helping people for nearly a century and has recently been updated for our modern world.
Now this won't help with the issue directly but it will help you build the skills to develop healthy relationships in the business world. I promise that if you use what is in this book your work environment will be a better place: How to Win Friends and Influence People: Updated for the Next Generation of Leaders
How to Win Friends and Influence People: Updated for the Next Generation of Leaders - Dale Carnegie. Technically it's his estate but his books and philosophies have been helping people build their careers since 1938. This book is the latest but I can't speak to it but if it's anything like the previous version it will be a goldmine of information.
I lead an O365 support team focusing on exchange online at MS.
RELAX
There will be plenty of training, we had 3 weeks worth before our agents even touched a ticket, if they were ready. Ours came in mostly by phone due to the client. Ask every question that comes to mind, you need the answer to those to feel comfortable. With it being remote understand you're going to have zoom trainings and documentation as your primary references. There should be a wiki too for quick reference. What you likely won't have is the ability to touch anything that you are walking your customer through so make sure you understand where things are in addition to being able to read the instructions.
The most important piece of advice I can give you is that while this is a technical role that comes secondary. The primary aspect of your role is customer service. Spend the next few weeks focusing on that because you won't get training on that on the job and if you do it's because there is an issue. I highly recommend reading Dale Carnegie's 'How to Win Friends and Influence People' it is a great book anyone in a customer-facing position should read, it's been teaching soft skills since 1938 and is a book that most people in senior leadership have read at least once. It teaches you how to connect and relate with people on a different level than most. Why is this important? Because you can have the right answer but if you can't convey it effectively you don't have an answer, you have an upset customer.
Pay close attention to your metrics, that is how you will be ranked and how your job performance will be judged. But don't focus on it so much that you're sick or worried, just be able to explain any outliers. If it's a ticket jump on that first contact message ASAP, that is a key metric. Never miss a scheduled SLA, even if you don't have an update, tell them you don't have an update and you will reach out when you do. Any metric related to customer communication will be heavily weighted, after all, it is your job to make sure they are happy.
The one I linked to, it was just released in May. The full title it 'How to Win Friends and Influence People: Updated for the Next Generation of Leaders' I grabbed the audio book and its next on my list.
There is also one from 2012 that focuses on online presences called 'How to Win Friends and Influence People in the Digital Age' that i'm currently working through.