Index out of bound error when setting masses

I have a data file whose heading lines are

data.lmp (written by ASE)

192      atoms
2  atom types
0.0                   12.42  xlo xhi
0.0                   12.42  ylo yhi
0.0                   12.42  zlo zhi


Atoms

     1   2      6.9118895378999996     -4.5982889290999998           13.0940229812
     2   1      6.4007004835999997     -4.6434328653000003      12.215485861299999
     3   1      7.0451269083000003     -3.6844772468000002           13.3189254954
     4   2           10.6028375513      2.5287524368000001      10.590542836799999
     5   1           11.1849460468      2.7084845534999999           11.3690123042
     6   1      9.9660310933999998      1.8797136509000001      10.873087679599999

As you can see the total atom type is 2.

Now I want to assign a different atom type to one of the H atom (id:6) so that I can use it in the pair coeff. And this is what I do

units           metal
atom_style      atomic
boundary p p p
neighbor 1.0 bin
box      tilt large

read_data data.lmp

mass 1 1.008
mass 2 15.999
# a new atom type 3
mass 3 1.008
change_box all triclinic

set atom 6 type 3

Then I get the following error

ERROR: Numeric index 3 is out of bounds (1-2) (src/input.cpp:1561)
Last command: mass 3 1.008

It looks to me like I cannot use a new atom type since the data file limit it to 2. What I can do to change it?

See the extra/* keywords in the documentation for read_data (read_data command — LAMMPS documentation)

Oh I see. Thank you.