Your best way will be rideshare or taxi.
Normally I'd say take the Skyliner to CBR, transfer to the Epcot line, then walk to Beach Club. (Skyliner AoA to CBR, transfer to DHS line, then walk or boat to Beach Club is a possibility but not as efficient.) However, I'm not sure how early Skyliner and boats will be running that day - would depend on what time DHS and Epcot open or if they start the Skyliner running early enough for guests to get to the Epcot area resorts for early breakfast ADRs.