The MSP portal allows MSP organizations to link organizations you managed to your place. Here is how it works
Go to the MSP Portal
Click "Link Organization" or "Add Organization"
Type in the Organization name and the admin email of that organization
The admin will receive a 6-digit code in their inbox
Use the 6-digit code
Once it is linked, you can click the "Login as user" icon on the right to jump into the organization as the admin account you just linked to.