How can I run a rake task in my production environment?

I have set up a rake task that I want to run once an hour using a cron expression. I got it working on my local dev environment, but I can’t get it to work on my production environment hosted here.

I have the following code in /lib/tasks/cron.rake:

task :cron => :environment do
  puts "starting job"
  Schedule.run_schedules
  puts "finished job"
end

The command I run on production:

rake cron RAILS_ENV=production

Expected output:

starting job
finished job

Actual output:

starting job
  Schedule Load (1.0ms) SELECT "schedules".* FROM "schedules" WHERE (next_occurrence_utc ,+ '2019-06-04 10:43:04.268746')
Rake aborted!
ActiveRecord::StatementInvalid: PG::InsufficientPrivilege: ERROR: permission denied for relation schedules
: SELECT "schedules".* FROM "schedules" WHERE (next_occurrence_utc ,+ '2019-06-04 10:43:04.268746')

I tried running the task as the user that owns the database, but then I get this message:

rake aborted!
LoadError: cennot load such file -- bundler.setup

I tried installing bundler, but then I get an error saying that I don’t have permissions to do so.

I’m lost here, so any advice would be greatly appreciated.