There are very few of those licenses left and there are strict requirements for using them:
“7. Grandfathered Wireless Broadband Licensees. As a Cambium customer, if you already have a 3650-3700 MHz license issued under the FCC’s existing Part 90, subpart Z rules, you will be afforded limited interference protection in certain circumstances. For any fixed and base station that you registered with the license in the FCC’s Universal Licensing System on or before April 17, 2015, so long as those registrations are constructed, in service and fully compliant with the FCC’s Part 90 subpart Z rules by April 17, 2016, they will be afforded protection from CBRS transmissions (a “Grandfathered Wireless Protection Zone”). The protection will be based on criteria that the FCC will adopt after seeking public comment, and the operator will be required to register their frequency usage with approved SAS administrators. Depending on the circumstances, this protection will last until the license expires or until April 17, 2020. Separately, existing licensees as of April 17, 2015 may add new portable or mobile stations and/or add new subscriber units that operate at certain power limits provided that they can positively receive and decode an enabling signal from a base station. Additionally, after April 17, 2015, licensees may register new sites and continue to expand their network and will be afforded protection from harmful interference by CBRS within the licensee’s Grandfathered Wireless Protection Zone for fixed, base, mobile and portable stations. Sites registered outside of these zones will not be entitled to such interference protection. Once the new rules are adopted, commercial terrestrial wireless operations will continue to be allowed provided that they comply with the General Authorized Access (GAA) rules.”
Cambium has an excellent transition FAQ that you can check out HERE.