To solve the problem at hand:
First, find out the name of the table to which the TOAST index belongs:
SELECT r.oid::regclass
FROM pg_class r
JOIN pg_class t ON r.reltoastrelid = t.oid
JOIN pg_index i ON t.oid = i.indrelid
JOIN pg_class ti ON i.indexrelid = ti.oid
WHERE ti.relname = 'pg_toast_2619_index'
AND ti.relnamespace = 'pg_toast'::regnamespace;
The answer should be pg_statistic
, the system catalog that stores table statistics.
Then, as superuser, reindex the table:
REINDEX TABLE pg_statistic;
To solve the bigger problem:
Find out what caused the index corruption:
Test your hardware, particularly storage and RAM.
Test if your storage processes a sync request correctly by writing the information to persistent storage rather than caching it where it can get lost.
Check if you had any crashes lately.
Move to a recent supported version of PostgreSQL and always apply bugfixes.