Clear it in 3 steps
Start the environment
Investigate the target
Submit the flag

The UDP datagram with IPv4 ID 0xbeef in fragments.pcap contains overlapping fragments that overwrite earlier bytes. Reassemble it using last-arriving bytes, then recover the flag from the Base64 data in the UDP payload.
IPv4 fragment offsets are in 8-byte units; focus on Identification 0xbeef
Write fragments into a reassembly buffer in capture order so later data overwrites overlaps
Remove the 8-byte UDP header and PAYLOAD= prefix, then Base64-decode