First, you need to change view to the Partner view at the top of your page. 

The next step is to click on the tab Administrators and consultants, then choose Consultants and finally click Add consultant.

Add all the information and choose which organizations under your partner the user should be attached to by clicking + Attach organization and check the boxes for the desired organizations.

The consultant is now added to the selected organizations. Press Save when your done. 

You can also connect more organizations to an already existing consultant on your partner. Go to Administrators and consultants and click on the 3 dots to the right of the consultant.

Choose Edit consultant and then click on + Attach organization and check the boxes for the desired organizations.

Press Save when your'e done.