If you would like to restore a module that you had previously removed, no problem!

Step 1:

Go to Course setup > Content and (very important) - refresh the page.

Step 2:

Scroll down to find Add a New Module.

Step 3:

Start typing the name of the module you had removed.

Step 4:

You will now see an option to "undelete" a module.

E.g.

Step 5:

Click on that and your module will be back!