Using NIST SP 800 - 90Ar1 Test Vectors for HMAC_DRBG with Reseeding and AdditionalInput
The other two AdditionalInput are to be used with the Generate function.

Page 47 of the spec describes it.

Step 2 of the algorithm performs:

 If additional_input ≠ Null then (Key, V) = HMAC_DRBG_Update (additional_input, Key, V)


Now, you might wonder why there are two strings AdditionalInput. Well, as described in the test spec there are two calls to the generate function for each test vector, so you have two additional inputs.
Note that only the second output of the generate is printed in the test vector.