To find out if your research lab, department, university of company is already a member, check the List of current institutional members with number of current submissions/publications (JMIR website).
Note that certain membership types have limitations on the number of APF/APC waivers granted per year (see link to membership types below).
In the member table, you can see how many manuscripts from the member have already been published or are under review. APF/APC waivers are granted on a first-accepted first-serve basis. You should be prepared to cover the APF/APC from another source if the number of fee waivers for the member institution has been exceeded by the time your article has been accepted.
Speak to the contact listed in the table to suggest renewing a membership if it is expired, or upgrading the membership if the number of APF/APC waivers is exhausted.
If you cannot find your organization in the list, consider to set up one for your own lab or department, or speak to your research unit or department chair.
Institutional Membership Types (JMIR Website) - contains the "fine-print"