Cellular backup with AT&T microcell

Greetings! I live in an area with very poor cellular coverage and require a “microcell” to get service. The microcell requires registration of phone numbers authorized to access. How can I find a number for my Ring Base to authorize it on the microcell so that it can access the cell network in the event of going on backup. Without the microcell, I have 1 bar or less of cell service.