The full sentence is
見学を希望する場合は、一週間前までに担当者を通じて申し込んでください。
I want to know this 一週間前までに meaning. I tried thinking and came up with "within one week before (the deadline which is not mentioned)" but I'm not sure if it's correct.
Let's look at the different parts:
- までに usually refers to a hard deadline (e.g. "until ... at the latest")
- 見学 means (learning/training by) watching, for example watching a training session
- 一週間前 is to be understood as one week before the intended date of 見学 (e.g. watching the training session).
Putting it all together:
見学を希望する場合は、一週間前までに担当者を通じて申し込んでください。
For those wishing to watch [a training session / a lesson], please get in touch with the contact person at least a week in advance.
(You will have to adapt the translation of 見学 depending on the context.)
