I accidentally hid a contact on Google Maps, thereby removing his/her address on the map. How do I undo this action?
According to solutions given Google Maps Help forum, you can try deleting the contact and then re-adding it.
It is presumed that these settings are stored in the Contacts App on your phone, not the Maps app.
Thus perfoming the above mentioned workaround will then override the "hide" option.
Additionally you may need to resync the information to Google servers.
Open location sharing (from the menu in the top left corner of the Google maps app). You should see a list of everyone who has shared their location with you, including the one you accidentally hid from the map. Select that person, and an option should appear for you to "show on map". Select that, and they will again appear on your map.
on the maps app, click on your profile picture located at the right side of the search bar, then "location sharing", then click on the 3 dots in the top right corner and "hidden from map (1)" where 1 is the number of hidden contacts. Then, click on the 3 dots of the contact that you want to unhide, and click on "show on map". Now your contact's location will be shown on the map again.