How do I manually reset my MacBook?

Hi JohannaD2,

Welcome to the Apple Community.

Here are articles from Apple support that may help:

To reset Mac up like new

What to do before you sell, give away, or trade in your Mac - Apple Support

or

To use macOS Recovery to reinstall the Mac operating system

How to reinstall macOS - Apple Support

or

How to reset the  Systems Management Controller (SMC) on your Mac 

Reset the SMC of your Mac - Apple Support

or

How to reset the NVRAM/PRAM 

Reset NVRAM on your Mac - Apple Support

All the best :-)