I want to umount /var mount point and mount to another partition on linux but I am getting the error that the /var is in use, I got the recommendation to boot into a single user mode to perform this operation, I would like to know how I can do this. The server is running on Azure (VM)

I tried editing the /etc/default/grub file to increas the timeout for the option to show so I can edit the grub entry to boot into the single user mode, I was able to edit the entry but couldnt start the server