Use the INTERVAL type to it. E.g:
--yesterday
SELECT NOW() - INTERVAL '1 DAY';
--Unrelated to the question, but PostgreSQL also supports some shortcuts:
SELECT 'yesterday'::TIMESTAMP, 'tomorrow'::TIMESTAMP, 'allballs'::TIME;
Then you can do the following on your query:
SELECT
org_id,
count(accounts) AS COUNT,
((date_at) - INTERVAL '1 DAY') AS dateat
FROM
sourcetable
WHERE
date_at <= now() - INTERVAL '130 DAYS'
GROUP BY
org_id,
dateat;
You can append multiple operands. E.g.: how to get last day of current month?
SELECT date_trunc('MONTH', CURRENT_DATE) + INTERVAL '1 MONTH - 1 DAY';
You can also create an interval using make_interval function, useful when you need to create it at runtime (not using literals):
SELECT make_interval(days => 10 + 2);
SELECT make_interval(days => 1, hours => 2);
SELECT make_interval(0, 1, 0, 5, 0, 0, 0.0);