Just use the flag "-s" with the IPv6 address of the server as the argument.

$ ./dnsblast -s dead:face::2 -r 500 -q 2 -proto tls -noverify  -l 10

EXECUTING TEST
+-----------------------------------------------------------+
2020/03/17 23:26:15 QPS/Thread:  36  Latency:  32.141583ms
2020/03/17 23:26:16 QPS/Thread:  32  Latency:  70.730121ms
2020/03/17 23:26:17 QPS/Thread:  114  Latency:  33.450903ms
2020/03/17 23:26:18 QPS/Thread:  88  Latency:  57.15537ms
2020/03/17 23:26:19 QPS/Thread:  88  Latency:  73.337146ms
2020/03/17 23:26:20 QPS/Thread:  42  Latency:  182.624116ms
2020/03/17 23:26:21 QPS/Thread:  34  Latency:  258.311857ms
2020/03/17 23:26:22 QPS/Thread:  34  Latency:  292.833628ms
2020/03/17 23:26:23 QPS/Thread:  36  Latency:  309.374108ms
2020/03/17 23:26:24 QPS/Thread:  236  Latency:  54.491316ms
2020/03/17 23:26:25 QPS/Thread:  88  Latency:  158.465191ms
2020/03/17 23:26:26 QPS/Thread:  46  Latency:  328.005638ms
2020/03/17 23:26:27 QPS/Thread:  44  Latency:  370.920222ms
+-----------------------------------------------------------+

  REPORT
+---------------------+------------------------+
| Target Server       | tls://dead:face::2:853 |
| Test                | Uncached Responses     |
| Send Rate           | 500 Queries/Sec        |
| Threads             | 2                      |
| Duration of test    | 10 Sec                 |
| Protocol            | TCP-TLS                |
| Average Queries/Sec | 196                    |
| Average Latency     | 53.629597ms            |
+---------------------+------------------------+