The following steps can be followed to give a user access to a Data Gateway in Power Automate:

1. Access Power Platform admin center at https://admin.powerplatform.microsoft.com/
2. Go to "Data gateways (preview)"
3. A list of gateways will be displayed. Click on the 3 dots menu col (...) and select "Manage users"
4. In the "Enter a name or email address" box enter the user name
5. Press the "Share" button

The user should then be able to use the Data Gateway in Power Automate.