To change the date (and time) of a note all you need to do is insert the desired date and time at the very beginning of your note. The important thing about editing the date is to get the format right.
The /tap date format is
YYYY-MM-DD HH:MM. For example 2PM on January 30, 2021 would be 2021-01-30 14:00. /tap will let you know the date is in the correct format by highlighting it when it's detected, see example below.
The date must be included in the note at the absolute beginning, before Folders and Todos.