The best way to distribute Pickit to more of your colleagues is through a "Centralized Deployment". That means your Microsoft 365 administrator can install it to everyone in the organization or to specific people.
Read here to determine if a centralized deployment works for your organization.
If you want to manually invite users to your Business image bank, go to the "Content Administration" page on the web, navigate to your company name in the top left, choose "Invite People" and fill in their emails in the field, one email per row.
Only administrators and the image bank owner can invite new people.