As of PostGIS 2.3, the postgis extension was changed to no longer allow relocation. All function calls within the extension are now schema qualified.
While this change fixed some issues with database restore, it created the issue of if you installed PostGIS in a schema other than the one you wanted to it is not intuitive how to move it to a different schema. Luckily there is a way to do this.
For this exercise, I will install PostGIS in the default schema and then demonstrate how to move it into another schema location.
You can run these steps using psql or pgAdmin or any other PostgreSQL tool you want.