How can I add custom 301 redirections after a phpbb import?

I’ve imported a phpbb forum to Discourse.
After the import, I’ve merged a lot of categories. I would like to redirect the old phpbb links to this new category.

How can I add such 301 redirections in Discourse?

Well I should search more than 5 min before starting a topic I guess.

edit : well my questions is now more like “How can I edit a redirection”, since there are actually already redirections:

[1] pry(main)> Permalink.create(url: '/viewforum.php?f=15', category_id: 80)
ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_permalinks_on_url"
DETAIL:  Key (url)=(viewforum.php?f=15) already exists.
: INSERT INTO "permalinks" ("url", "category_id", "created_at", "updated_at") VALUES ('viewforum.php?f=15', 80, '2018-06-23 19:48:22.967909', '2018-06-23 19:48:22.967909') RETURNING "id"
from /var/www/discourse/vendor/bundle/ruby/2.5.0/gems/rack-mini-profiler-1.0.0/lib/patches/db/pg.rb:92:in `async_exec'

The redirection is wrong though, I need to change the target. Any idea?

edit : okay, go to the “customize” admin section. \o/