Is this the first pre-email asking for your details? If it is, you should get login credentials after replying. Depending on VO and luck, you'll get the login details between 1 and 14 days... Otherwise, contact IRCC by replying to the email again, and raise a webform.
A number of people are reporting reminder emails like this, appears to be a glitch. The suggestion is to keep replying as you get them. In my case, I am still waiting for login credentials since the 11th, but did not get any reminder emails.
There are clearly bugs in the system, and really inconsistent wait times at this stage. I thought once pr is approved, it would be a simple process...but of course this is the IRCC, can't be straightforward!!