If you do not have an external keyboard or cannot access the USB ports in the back of the unit, you can use the Windows On-Screen Keyboard.

To open the On-Screen Keyboard in Windows 7:

On Windows 7, you can open the on-screen keyboard by clicking the Start button, selecting “All Programs,” and navigating to Accessories > Ease of Access > On-Screen Keyboard.

Instructions for opening the OSK in Windows 7

To open the On-Screen Keyboard in Windows 10:

Go to Start , then select Settings  > Ease of Access  > Keyboard, and turn on the toggle under Use the On-Screen Keyboard. A keyboard that can be used to move around the screen and enter text will appear on the screen. The keyboard will remain on the screen until you close it.

https://support.microsoft.com/en-gb/help/10762/windows-use-on-screen-keyboard

You can set the OSK to open on startup, Select the Start button, then select Settings > Apps > Startup.