on your Mac.Click the reminder you want to add a tag to, then do any of the following:
Add a tag to the tag field: Click the Add Tags field, then choose a tag. If the tag you want doesn’t exist, enter # followed by a word to create and apply a new tag.
Add a tag to the title or notes: Enter # in the title or notes field of the reminder, then choose a tag. If a tag you want doesn’t exist, enter a new word to create and apply a new tag.
Add a tag using the Tag button : Click
on your Mac.Scroll to the Tags section of the sidebar.
Do one of the following
View all reminders with tags: Click All Tags.
View all untagged reminders: Click All Tags twice, so that All Tags is crossed out.
View reminders by selected tags
See a list of reminders that meet the tag criteria you select.
Go to the Reminders app
on your Mac.Scroll to the Tags section of the sidebar.
Control-click a tag, then choose Rename Tag.
Enter a new name for the tag, then click OK.
If the name you enter is already used by another tag, you’re notified. You can then choose either Replace Tag or Discard Change.
When you rename a tag, it’s changed in all reminders and Smart Lists that use it.
Tip: To merge tags, rename a tag to one that’s already in use. For example, if you have a tag named #Home and a tag named #House, you can rename #House to #Home so that #Home is used in all places that #House was used previously.
To learn more about using tags, go to the Reminders app Create custom Smart Lists in Reminders on Mac