Employer must to submit the information of your job offer and pay $230 compliance fee for your work permit, because you are exempted of LMIA. Company will have a number of the job offer thereafter you will be able to submit your application to extend your closed work permit.I already have that letter.
They gave me at the time of my PNP.
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/partners-service-providers/employer-portal.html