how to format my hard drive without a boot disk

Note that some USB drives don't have the option to be initialized, they just get formatted and a drive letter.

If the disk is listed as Offline, first right-click it and select Online. In Disk Management, right-click the disk you want to initialize, and then click Initialize Disk (shown here). If you can't open it as an administrator, type Computer Management instead, and then go to Storage > Disk Management.

To do so, in the search box on the taskbar, type Disk Management, select and hold (or right-click) Disk Management, then select Run as administrator > Yes. Open Disk Management with administrator permissions. If you prefer using PowerShell, use the initialize-disk cmdlet instead. Here's how to initialize a new disk using Disk Management. Instead we recommend troubleshooting the disk to see if you can read the files - see A disk's status is Not Initialized or the disk is missing entirely. If your disk already has files on it that you care about, don't initialize it - you'll lose all the files.

How to format my hard drive without a boot disk