You will need the Limited Write Financial permission to perform this action.
Navigate to "Contributions > Envelopes" in the left hand navigation menu and click on "Add New" near the top.
A pop up will appear with the following fields.
Envelope # - the envelope number to assign. Click on "autogenerate" to have the system provide an unused number.
Person - the person this number should be assigned to.
Once you fill out the fields, click on "Assign" to finish. You can check "Keep open and assign another" when adding multiple envelope numbers.
The same envelope number can be assigned to multiple people.
You can also assign an envelope number when editing/adding a person from the "Giving" tab in the pop up.
You can edit an existing giving envelope by clicking on "Edit" at the end of a row containing the envelope you want to edit. You can change the number and even reassign it to a different person. Reassigning a giving envelope number does not affect any previously entered transactions.